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Chemistry

The Art Institute of California

Ariana Nussdorf

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What is Chemistry?

A love connection? Drugs?

Chemistry is all around us!

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What is science?

Science is the art of understanding the world around us.

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Branches of science

• Science is is used to study a certain area of interest. Some topics include:– Anthropology: the study of human cultures both

past and present – Biology: the science that studies living organisms– Chemistry: the science of matter and its

interactions with energy and itself – Computer Science: the systematic study of

computing systems and computation– Physics: the study of the behavior and properties

of matter

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The science of this class

• In this class, we will not attempt to cover all aspects of science.

• Instead, we will focus on chemistry, the most fundamental science.

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What is Chemistry?

Chemistry is a science that focuses on why things are the way they are because of the small particles that make up the substance.

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What do you mean particles?

Particles can be big enough to see (hair, bits of dust) or so tiny that we can’t see it (air, gas).

Macroscopic: visible with the naked eye Microscopic: too small to see without

the aid of a microscope

“macro” means big (big mac, mac daddy, macroeconomics)“micro” means small (micromachines, microeconomics)“scopic” has do do with sight or vision (microscope)

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If we can’t see it how do we know it’s there?

• What do you have to fill a balloon with in order to get it to float? ________

• What happens if you blow up a balloon with your own breath?_________

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We can’t see it but it’s there!

Filling a balloon with helium or just air from your breath has a different effect on the balloon because helium and air are different microscopic particles with different properties even though we can’t see them!

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Zooming in with Chemistry

• The study of chemistry is a system to explain matter beneath what we see.

• Suppose Google Earth could zoom into the graphite of a pencil. We would find that all matter is made up of microscopic particles connected together like bricks forming a wall.

Matter: “stuff”; anything that takes up space including tiny particles that we can’t even see with the naked eye.

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It Takes Two!

Fill in the blanks:There is day and there is ______There is good and there is ______There is on and there is ______There is positive and there is ______

There are always two opposing forces.Without one we wouldn’t notice the other!

Existence is based on a balance of two opposing forces, even on the microscopic level.

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Positive and Negative

• Even on the smallest scale, there is still a balance of two opposing forces. In chemistry, these opposing forces are positive and negative.

• The tiniest particle of matter is a negative particle called an electron, symbolized by e-.

• To oppose this force, there is also a positive particle called a proton, symbolized by p+.

• All matter comes from the balance of positive protons and negative electrons.

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Let’s Review!

• Chemistry focuses on understanding microscopic particles.

• These microscopic particles are made up of positive protons, “p+” and negative electrons, “e-” which represent opposing forces on the smallest scale.

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Try These 1.1

• Before you move on, make sure you understand the following concepts:– What is chemistry?– What is the difference between microscopic and

macroscopic particles?– What is matter?– Why does it make sense that microscopic

particles are positive and negative?– What is a proton and what is an electron and how

do you symbolize them?

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Protons, Electrons, Neutrons

• There is one more microscopic particle that is important in understanding what makes up matter: the neutron, symbolized by n0.

• Neutrons are not positive or negative. Neutrons are neutral.

– Protons are the tiniest positive particles– Electrons are the tiniest negative particles– Neutrons are the tiniest neutral particles

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Remembering e-, p+, n0

• Here’s a trick I use to remember the charges for electrons, protons, and neutrons.

• Electrons:– When you write the letter “e” you usually start by drawing a

horizontal line which looks like a negative symbol.

• Protons:– When you write the word “proton” the 4th letter is a t which

sort of looks like a positive symbol.

• Neutrons– Neutron has the word “neutr” in it which is the beginning of

the word “neutral”.

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Protons, Electrons, Neutrons

• Protons, neutrons, and electrons come together in a specific way.

• The protons and neutrons clump together and the electrons float around them like a fly moving around a piece of rotten fruit.

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The Atom

The solar system describes the planets orbiting around the sun.

The atom describes the e- orbiting around the p+ and n0.

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Anatomy Of An Atom

• The central region of the atom consisting of p+ and n0 is called the nucleus of the atom.

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Anatomy Of An Atom

• Overall, the nucleus is positive because the protons are positive and the neutrons don’t have a charge.

• The negative electrons orbit around the positive nucleus.

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Try These 1.2

• Before you move on, make sure you understand the following concepts:– What is an atom?– What are the pieces that make up an atom?– What’s the difference between a neutron and a

nucleus?– Draw your own picture of an atom.

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Elements• If an atom is like a scoop of ice cream,

an element is the flavor that the ice cream can be.

• Elements are just atoms with a specific number of protons just like chocolate ice cream is ice cream with the specific properties of chocolate.

• The term atom and element can be used interchangeably just like you can say ice cream or you can be more specific and say chocolate ice cream.

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Elements

• Every element has its own amount of protons.• You cannot change the number of protons or else

you would have a different element.• You can change other aspects of an element, like

how many neutrons or electrons it has, but the number of protons an element has is constant. – The element Neon has exactly 10 protons and that cannot

be changed. If an element only has 9 protons it would not be Neon.

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Molecule

• When you combine elements together you form molecules.

• A common molecule is the water molecule.

• Water or “H 2 O” is a combination of two H elements with an O element.

element + element = molecule

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Matter

• The matter that we see is made up of specific atoms, or elements, combining to form trillions of molecules.

• We may not be able to see one H or O element, or even one H2O molecule but we can see water as matter when there are enough H2O molecules together.

molecules + molecules = matter

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Matter is the story!

• A story is made up of specific letters arranged to from words which make sentences that form a story.

• Matter is made up of atoms specifically arranged as elements which combine to form the molecules that make matter.Letters → word → sentence → story

atom → element → molecule → matter

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Try These 1.3

• Test your understanding:– If one atom has 3 protons and one atom has 3

protons, are they the same element?– If one atom has 6 protons and one atom has 4

protons, are they the same element?– If a molecule changes the number of electrons it

has is it still the same molecule?– What’s the difference between an atom and an

element?– What’s the difference between a molecule and

matter?

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The Periodic Table of Elements

• For reference, all elements are organized in a table called the periodic table.

Each box represents a unique element with a unique number of protons

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The Periodic Table: Chemistry’s Map

The periodic table is like a color coded map. It is a resource that gives information about each element based on the properties specific to each element.

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Why the odd shape?

• The periodic table would look a lot nicer if it was a normal rectangle but there is a reason for its odd shape.

• Each vertical column of elements are related in some way and each horizontal row of elements are related in another way.

Elements in this row have something in

common

Elements in this column have something in

common

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• The English name: hydrogen H

• The Greek or Latin name: ferrum (iron) Fe

• Their place of discovery: europium E

• A scientist: curium Cm

Chemical Symbol

• Each element is given an alphabetical symbol.• Symbols are an abbreviation of the chemical name

which can be based on:

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The Periodic Table

• The symbol is always given by a capital letter.• If there are two letters in the symbol for the element,

the first is capitalized and the 2nd is lower case.

Carbon C

Chlorine Cl

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Understanding the Periodic Table

Atomic/chemical symbol

Atomic Number (number of protons)

Atomic Weight (protons + neutrons)

Atomic name

Most periodic tables give the same basic information about each element

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Atomic Number

• Since all elements have a unique number of protons, an atom’s number of protons defines which atom it is. – An atom with 6 protons must be carbon because only

carbon has 6 protons.– An atom with 1 proton must be hydrogen because only

hydrogen has 1 proton.

Atomic Number = number of

protons

Use the periodic table to find out how many protons an element/atom has!

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Atomic Number

• Since all elements have a unique number of protons, an atom’s number of protons defines which atom it is. – An atom with 6 protons must be carbon because only

carbon has 6 protons.– An atom with 1 proton must be hydrogen because only

hydrogen has 1 proton.

• An atom’s atomic number is just how many protons that atom has.

• Unless otherwise specified (by charge or weight), the amount of protons, electrons and neutrons are equal.

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Atomic Weight

• Protons, electrons, and neutrons are extremely small but they actually still have weight.

• The weight of these particles are too small to be measured by pounds or grams so an even smaller unit is used to describe their weight, amu, which stands for atomic mass unit.

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Atomic Mass

• Electrons hardly weigh anything so most of the weight of an atom comes from protons and neutrons.

1 proton weighs 1 amu1 neutron weighs 1 amu

• Since an element cannot change how many protons it has, the only way to change the weight of an element is by changing the number of neutrons.

• Isotopes are atoms that only differ in the amount of neutrons they have but the number of protons remains unchanged, therefore the weight is different.

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Keep In Mind

• Atomic mass = protons + neutrons– Protons and neutrons make up most of the weight

of the atom because electrons are too small to contribute to weight.

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Try These 1.4

• Test your understanding:– Why are some atomic symbols obvious (carbon = C) while

others are not (Iron = Fe)?– What is an element’s atomic number?– Can two different elements have the same atomic

number?– If an atom has an atomic number of 4, how many protons

does it have? How many electrons does it have?– Approximately how much would an atom weigh with 6

protons and 6 neutrons?– Which element has exactly 8 protons? (refer to the

periodic table)– What’s an isotope?

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Atomic Charge

• Each proton has a charge of +1 • Each electron has a charge of -1 • Each neutron has no charge (but it’s still important

because it has weight).

• If an atom has 8 p+ and 8 e-:8 protons x (+1) = +88 electrons x (-1) = -8 total charge = 0

This atom would be considered neutral because it has the same number of positive protons and negative electrons.

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Atomic Charge

• An element cannot change the number of protons it has but it can change the number of electrons it has.

• An ion is a charged atom, it is charged because it has extra electrons or is missing electrons.

• If an ion has 11 p+ and 10 e-:11 protons x (+1) = +1110 electrons x (-1) = -10 total charge = +1

This atom would be considered to have a +1 charge because it is missing one negative.

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Positive/Negative/Neutral

• If an ion is negative it has extra electrons.

• If an ion is positive it is missing electrons.– The symbol for an ion or an atom is written in the

following way:

O-2 Na+ or Na+1 CAtomic symbol

Charge written as a superscript

If the charge is +1 or -1 it’s not necessary to write the “1”

No charge is written if the atom is

neutral

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Positive/Negative/Neutral

O-2 Na+ or Na+1 C

This oxygen has 2 extra negative

electrons

These atoms are missing one

electron

This carbon is neutral so it has

the same amount of

electrons and protons

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Charges• Why does -1 mean 1 extra electron and +1

mean 1 missing an electron?– Electrons are negative so if your overall charge is

negative, you must have extra negatives. If your overall charge is positive, you must be missing negatives.

+ ++

- --

+ ++

- --

+ ++

- --+3 - 3 = 0

Positives and negatives cancel

out: neutral

+3 - 2 = +1Missing an

electron, there’s a leftover positive

charge: +1

+3 - 4 = -1Extra electron,

extra negative: -1

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Keep In Mind

Atomic mass = protons + neutrons– Protons and neutrons make up most of the

weight of the atom because electrons are too small to contribute to weight

Vs.Atomic charge = protons - electrons

– Protons are positively charged and electrons are negatively charged. Neutrons are neutral so they don’t contribute to charge.

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Determining Charge• What is the charge on a Potassium (K) atom

with 18 electrons?– Find the atom on the periodic table

• K is element number 19

– The atomic number is the number of protons it has (that’s the number of positive charges it has)

• K has 19 protons

– Atomic charge = protons - electrons (in this question the number of electrons were given)

• The charge on K = 19 protons - 18 electrons = +1

– Write your answer in the correct format• K+1

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Determining Electrons

• How many electrons does a S-2 have?– Use the periodic table to determine the number of

protons the atom would have in it’s neutral state. • Sulfur is atom #16 so it has 16 protons.

– Remember “-” means extra electrons “+” means missing electrons.

• S-2 has 2 extra electrons so instead of having 16 electrons to match 16 protons, it has 16+2= 18 electrons.

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Try These 1.5

• Be sure to understand the charge of an ion:– What is the difference between and atom and an

ion?– How many electrons are missing or extra if a

charge on an ion is +3? If the charge is -1?– What is the charge on an ion with 5 protons and 8

electrons?– Write the symbol for Floruine with a -1 charge.– What is the charge on calcium with 18 electrons?– How many electrons does Na+1 have?

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Electrons Around The Nucleus

• When runners race around a racetrack they use lanes so they don’t bump into each other.

• Similarly, electrons have lanes, called orbits or orbitals that they stay in as they rotate around the nucleus.

Orbital: The lanes for electrons around the nucleus

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Electrons Around the Nucleus

• Electrons rotate around the nucleus of an atom because the nucleus is positive (from the p+) and the electrons are negative so the negative electrons are drawn toward the positive protons in the nucleus.

Orbitals

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Bohr Model

• We use a birds eye view to show the electrons orbiting around the nucleus.

• We call this the Bohr model, named after Niels Bohr, the scientist that developed this way of looking at an atom.

First orbital

Second orbital

Third orbital

Remember: Bohr model looks like a bulls-eye

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Orbitals• Each orbital has an optimal amount of

electrons that can fit in it.– The 1st orbital can hold up to 2 electrons– The 2nd orbital can hold up to 8 electrons– The 3rd orbital can hold up to 8 electrons– The 4th orbital can hold up to 18 electrons

• The further out you go, the more room the orbitals have for electrons.

2 8 818

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Bohr ModelFirst orbital with it’s max of 2 electrons

Second orbital with it’s max of 8

electrons

Third orbital with it’s max of 8 electronsUse dots to

represent the electrons

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Filling The Orbitals

• Electrons fill up the first orbital before they fill up the second orbital and then fill up the second orbital before the fill up the third orbital and so on.

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Try These 1.6• Make sure you understand how electrons

rotate around the nucleus according to the Bohr model.– Why do electrons rotate around the nucleus in

lanes called orbitals?– What’s the max number of electrons in the first

shell? In the second shell? In the third shell?– Draw a Bohr model of an atom with 1 electron– Draw a Bohr model of an atom with 5 electrons– Draw a Bohr model of an atom with 10 electrons

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Drawing Bohr Models

• We can draw Bohr models for specific atoms or ions.

Note: when you draw Bohr models you don’t have to show the p+ or n0, just show the electrons as dots in

orbital rings.

HeliumHydrogen Lithium

Sodium

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Drawing Bohr Models

• Let’s draw the Bohr model of Sodium with a charge of +1.– Determine the number of protons

• According to the periodic table sodium has 11 protons.

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Drawing Bohr Models

• Let’s draw the Bohr model of Sodium with a charge of +1– Determine the number of electrons

• A charge of +1 means sodium is missing 1 electron so instead of having 11 p+ and 11 e- it only has 10 electrons.

Remember: If an ion is negative it has extra

electrons.If an ion is positive it is missing electrons.

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Drawing Bohr Models

• Let’s draw the Bohr model of Sodium with a charge of +1– Fill the Bohr model with the appropriate number

of electrons. • Remember, the first 2 electrons go in the first orbital

before the next orbital can be filled.

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Try These 1.7

• Make sure you can draw the Bohr model of an atom or an ion.– Draw a Bohr Model for each atom or ion.

C F F-1

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Valence Electrons

• Valence electrons are the electrons contained in the outermost orbital of an atom.

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Valence Electrons

• We can determine how many valence electrons an atom or an ion has by looking at the Bohr model of that atom or ion.

Hydrogen1 valence electron

Sodium1 valence electron

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Try These 1.8

• Make sure you understand what the valence electrons are.– Draw a Bohr Model for each atom and determine

how many valence electrons it has.Magnesium Nitrogen Oxygen

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Valence Electrons

• What column of the periodic table is magnesium in? is nitrogen in? is oxygen in?

Mg: ____ N: ____ O: ____

• What connection can you make about the number of valence electrons an element has and its column/group number, located at the top of each column in the periodic table (1A, 2A…7A, 8A)?

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Valence Electrons and the Periodic Table

Atoms with 1 valence electron

Atoms with 8 valence electrons

Atoms with 3 valence electrons

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Optimal Valence

• Let’s say you are going on a road trip with friends.What’s the optimal number of people to take in your car?_________

What should you do if there are too many people who want to go? ______________

What should you do if there are too few people who want to go? ____________________

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2 8 818

Just like there is a specific number of people that can fit in your car that would make you happy on a road trip, there is a specific number of electrons that can fit in each orbital that would make the atom “happy”.

Optimal Valence

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Full Valence Rule • Molecules are more stable when their valence

shells are filled (filled with 2 electrons in the first orbital, filled with 8 electrons in the second, etc.).

• The reason why atoms can be charged is because atoms gain or lose electrons in order to achieve a full valence and be stable.

Valence not filled to max capacity

Atom is unstable.

Instead of gaining 7 more e-, just lose the

extra e-. New valence is full. Atom is stable.

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Achieving Full Valence

• Atoms may gain e- to make sure the valence orbital is full and therefore the atom is “happy” or stable.

• Gaining electrons causes the atom to become negatively charged.

Valence = 7 (unstable) Valence = 8 (now stable)

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Achieving Full Valence

• Atoms may lose e- to make sure the valence orbital is full and therefore the atom is “happy” or stable.

• Losing electrons causes the atom to become positively charged.

Valence = 1 (unstable) Valence = 8 (now stable)

(no more e- in this orbital anymore so the orbital below is now the outer most

orbital)

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Try These 1.9

• Make sure you understand the full valence rule.– What is the full valence rule?– Why do some orbitals need 8 electrons to be

stable while others need 2 or 18 or some other amount?

– What do atoms do to become stable and how does that affect their charge?

– Draw the Bohr models for O+2 and O-2. Which is more stable?

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WHY BOTHER?!?In this class we are going to figure out why a lot of stuff is the way it is. By zooming in to “the tree” and then zooming out to see “the forest”, we can truly understand the big picture.

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For the QuizMake sure you are able to: Understand the different terms used in chemistry. Draw an atom and label its parts and the significance of each part. Determine the ion based on the number of protons and electrons it has. Determine the number of protons and electrons based on what ion is stated Draw a Bohr model and use it to determine if an atom or ion is stable.