CHEMISTRY:The Study of Matter

Describing Matter

• Chemistry: study of matter• Matter: has mass and takes up space• Types of matter:

– pure substances (sugar, salt)– not pure substances (milk, fruit)

States of Matter: GASES

• Volume can change easily• Gas particles spread apart filling all of the

space available• Do not have a definite shape or a definite

volume

GAS BEHAVIOR

• Boyle’s Law: – Increased pressure= decreased volume.

Decreased pressure= increased volume.

GAS BEHAVIOR

• Charles’ Law: – Increased temperature = increased volume

Decreased temperature = decreased volume

IN SUMMARY….

• Gases at high temperatures have high pressure and a larger volume

• Gases at low temperatures have low pressure and low volumes.

States of Matter: SOLIDS AND LIQUIDS

• Solids: definite shape, definite volume.• Liquids: definite volume, but no shape

solids liquids

States of Matter: SOLIDS AND LIQUIDS

• Like gases, solids and liquids expand when heated and shrink when cooled.

• What evidence do you have of this?

• Can you think of an exception?

Changing State

melting

freezing

evaporating

condensing

deposition

sublimation

Describing Matter

• Atoms: The most basic particles that make up matter

• Elements: pure substances

Cannot be broken down into

smaller pieces

protons

neutrons

Describing Matter

• Compounds: two or more elements chemically combined (NaCl,sodium chloride, table salt)

• Mixtures: two or more substances, not in a specific pattern (salad dressing, dirt).– can be homogeneous (same throughout- salt

water) or heterogeneous (not the same throughout- salad dressing)

Measuring Matter

• Weight: how gravity affects the matter in an object

• Mass: the amount of matter in an object, not affected by gravity (unit= gram)

• Volume: the amount of space matter occupies (unit = milliliter, liter)

• Density: how tightly matter is packed into a given space (unit = gram / ml or l)

Density = Mass / Volume

Describing Matter

• Two Properties of Matter:– Physical Properties: observed without the

matter changing (state of matter, color, texture, flexibility, solubility)

- Chemical Properties: observed when matter changes into new substances (flammability, reactivity)

Changes in Matter

• Physical Changes: changes the form or appearance of matter, but does not make the matter into a new substance (ice melting)– Phase changes are physical changes

melting

freezing

evaporating

condensing

deposition

sublimation

Changes in Matter

• Chemical Changes: Produces new substances (candle burning).

Density

• Density relates the mass of a material in a given volume.

• Density = Mass ÷ Volume (g/mL)• Objects with a HIGH density will sink in

water• Objects with a LOW density will float in

water

Atoms and the Periodic Table

• Atom: smallest particle of an element• Have three, subatomic particles: protons

(+), neutrons (), and electrons (-). • Protons and neutrons: in the center of an

atom (nucleus) surrounded by electrons in a cloud.

Scale and Size of Atoms

• Amazingly small• Tiniest speck of dust contains 10 million

billion atoms

Atomic Number

• Every atom of an element has the same number of protons.

• Unique number of protons = atomic number.

• Atomic number identifies an element. Carbon (C) = 6, Oxygen (O) = 8, Iron (Fe) = 26.

• If an atom has to be stable, how can you figure out the number of electrons?

Organization of the Periodic Table

• Properties of an element can be predicted from its location on the PT

• Periods: Horizontal rows on the PT (elements lose reactivity as you move across periodic table, until you reach the gases)

• Groups: Vertical columns on the PT (elements in groups have similar properties)

Reading an Element’s Square

Metals

• Physical Properties: shiny, malleable (bendable), ductile (stretchy), conductive (transfers heat or electricity)

• Chemical Properties: react by losing electrons to other atoms (the fewer electrons to lose or gain, the more reactive an element is)

Metals

• Some are extremely reactive (sodium) others are not reactive at all (gold, platinum)

• Some have moderate reactivity (iron- corrosive)

• Reactivity decreases as you move from left to right across the periodic table

Alkali Metals

Group 1: react with other elements by losing one electron.

-So reactive, never found as uncombined elements in nature

-Two most important: Sodium and potassium

Alkaline Earth Metals

• Group 2• React by losing two electrons• Two most common are magnesium

and calcium• Each is fairly hard, gray-white, and a

good conductor

Transition Metals

• Metals in Groups 3-12• Most of familiar metals (iron, platinum,

copper, nickel, silver, gold)• Most are hard and shiny, good conductors• Less reactive as you move to the right

Misc. Metals

• Some elements in groups 13 and 14 (aluminum, tin, lead)

• Not very reactive• Lanthanides (top row in rows below PT):

soft, malleable, shiny, highly conductive). • Actinides (row below Lanthanides): Only

Actinium (Ac), Thorium (Th), Protactinium (Pa) and Uranium (U) occur naturally

Nonmetals

• Nonmetal: lacks most of the

properties of a metal (not

conductive, reactive, dull, brittle)• Carbon Family (group 14):

Elements can gain, lose, or

share four electrons• Very versatile

Nonmetals

• Nitrogen Family (group 15): • Gain 3 electrons• Occur in nature in the form of

diatomic molecules

(Di = two, atomic = of atoms).

Ex: P2,N2,

Nonmetals

• Oxygen Family (group 16): • Gains or shares 2 electrons• Because oxygen is highly reactive,

it can combine with most other

elements in nature• Oxygen you breathe is diatomic

O2, or can be triatomic, O3, ozone.

Nonmetals

• Halogen Family (group 17): Halogen means salt-forming (bonds to metals to form salts)

• Gains 1 electron– Very reactive, dangerous (but can bond to

other elements to be useful)

Nonmetals

• Noble Gases (group 18): Stable– Exist in the Earth’s atmosphere in small

amounts– Don’t bond to other elements (have

enough electrons)

Hydrogen

• Simplest element with the smallest atoms• Unique properties, cannot be grouped with

other gases• Makes up 1% of Earth’s crust• Rarely found on Earth as pure element• Mostly found as H20 (water)

Metalloids

• Characteristics of metals and non-metals• Most common is Silicon (Si)• Most useful property is their varying ability

to conduct electricity• Semiconductors (used in computer chips)

are made of metalloids

Isotopes

• Isotopes: identified by the mass number of an element (the number of protons plus neutrons)

• Carbon is most commonly C-12, but can be C-13 and C-14. What’s the difference?

Isotopes and Mass Number

• Atoms of an element always have the same number of protons, but can have different numbers of neutrons.

• Atoms of an element with different numbers of neutrons: isotopes

Phase Changes and Energy

• The phase a substance depends on the kinetic energy of the molecules

• Substances change from phase to phase in response to the input or output of energy

• Phase changes reflect a change in energy or a change in the behavior of the atoms or molecules, not a change on the atoms or molecules themselves.

• Ex: ice melting, water condensing

Phase Changes and Energy

• Matter can change from one state to another when thermal energy is absorbed or released.

Law of Conservation of Energy

• During any chemical or physical change, energy cannot be created or destroyed.

• Energy can change forms and can be transferred from one object to another, but the overall amount must be conserved.

Temperature

• A measure of the average kinetic energy of individual particles of matter

• Measured using a thermometer (heat increases the kinetic energy of the liquid inside, takes up more space).

Thermal Energy and Heat

• The total energy of all of the particles of an object is called Thermal Energy.

• The more particles an object has at a given temp, the greater the thermal energy.

• The transfer of thermal energy from matter at a higher temperature to matter at a lower temperature is called Heat.

• Why does ice melt in your hands?

Heat Transfer

• Heat is transferred in 3 ways: – Conduction: Heat is transferred without the

movement of the matter (metal handle of a pot getting hot).

– Convection: Heat is transferred by the movement of currents within a fluid (plate tectonics).

– Radiation: The transfer of energy by electromagnetic waves. Radiation does not require matter to transfer energy.

Examples of Heat Transfer

Direction of Heat Transfer

• Heat will flow from the warmer object to the colder object

• Heat transfer occurs in only one direction• In summary, heat always flows from higher

energy levels to lower energy levels.

Phase Changes and Energy

sublimation

deposition

melting

freezing

evaporating

condensing

Energy transferred TO the substance

Energy transferred FROM the substance

Calories

• Heat is measured in Calories. • 1 Calorie is the amount of heat needed to

raise the temperature of 1gram of water 1 degree Celsius.

• Equilibrium: when there is no net energy transfer within a system

Heat of Fusion

• Water molecules in ice are held together by forces called “bonds.”

• Energy is required to break the bonds when changing solid water (ice) to liquid water.

• The energy needed to change solid water to its liquid form is called Heat of Fusion.

• The Heat of Fusion for water = 80c/g (calories per gram)

Observing Chemical Change

• Matter has chemical and physical properties and undergoes chemical changes and physical changes.

Chemical Changes Occur When…

• Chemical changes occur when bonds break to form new bonds

• Chemical changes occur through chemical reactions

Evidence for Chemical Reactions

• Two main changes occur during a chemical reaction:– 1) Formation of new substances– 2) Changes in energy

Evidence for Formation of New Substances

• Color Change• Precipitate Formed (solid)• Gas Produced

Evidence for Changes in Energy

• Heat Produced (reactions can be exothermic or endothermic)

Matter and Energy

• When a reaction causes energy to be released (often as heat), the reaction is called exothermic. When energy is taken in, a reaction is called endothermic (ice melting).

Endothermic

Exothermic

Energy taken in, resulting temp is higher

Energy released, resulting temp is lower

Describing Chemical Reactions

• Chemical Equations: A short, easy way to show a chemical reaction, using symbols instead of words.

• Structure of Chemical Equations: All chemical equations have a common structure. Substances at the beginning are called “reactants” and substances at the end are called “products”

Chemical Equations

• reactant + reactant product + product• You read the arrow () as “yields.”

Law of Conservation of Mass

• Chemical Equations must be balanced because of the Law of Conservation of Mass (matter can neither be created nor destroyed)

Steps for Balancing Equations

1) Write the equation

H2 + O2 H2O reactants products

2) Count the atoms

H2 = 2 hydrogen atoms (reactant)

O2 = 2 oxygen atoms (reactant)

H2 = 2 hydrogen atoms (product)O = 1 oxygen atom (product)

Steps for Balancing Equations

3) Use coefficients to balance atoms (a coefficient is a number placed in front of a chemical formula to balance products and reactants)

H2 + O2 2H2O

**Coefficients can be placed on the reactant side or the product side of an equation

4) Look back and check

Checking your Equations

Chemical Reactions and Bonding

• Bonds are broken and formed during chemical reactions.

• If an atom loses or gains an electron it is called an ion (an element with a + or – charge).

• Bonds that form between ions are called ionic bonds (usually between metals and nonmetals).

Ionic Bonding

Chemical Reactions and Bonding

• If elements bond by sharing electrons, covalent bonds form.

• Covalent bonds usually form between nonmetals.

Covalent Bonds

Solutions

• Solutions: a well-mixed mixture.• Solvent: What does the dissolving (the

larger part of a solution).• Solute: What is dissolved (the smaller

part of a solution).

Liquid water solution

Concentration of a Solution

• Saturated Solution: A solution that contains as much solute dissolved as possible. (No more can be dissolved)

• Unsaturated Solution: A solution where more solute can still be dissolved.

Acids and Bases

• Properties of Acids: tastes sour, reacts with metals and carbonates, and turns litmus or pH paper red.

• Uses of Acids: vitamins,

batteries (sulfuric acid),

fertilizers

Acids and Bases

• Properties of Bases: taste bitter, slippery, turns indicator paper blue.

• Opposite of acids: Do NOT react with metals and carbonates

• Uses of Bases: • Cleaning Products

Acids and Bases

• The pH scale used to determine

the strength of an acid or a base. • The pH scale measures the

concentration of hydrogen ions

in a solution.• A low pH: very acidic.• A neutral solution (water) pH = 7• A high pH: very basic.

Acid-Base Reactions

• When an acid and base react, the product is neither acidic or basic.

• Neutralization occurs when an acid and base react (pH becomes closer to neutral)

• Salts form as a product of an acid base reaction when the positive ion in a base bonds with a negative ion of an acid.

• Ex: HCl + NaOH H2O + (Na+ + Cl-)