THIS IS A STUDY GUIDE, NOT AN ALL INCLUSIVE REVIEW.

THERE MIGHT BE THINGS NOT COVERED BY THIS STUDY GUIDE THAT MIGHT BE ASKED IN YOUR QUIZZES and TESTS.

STUDENTS ARE RESPONSIBLE FOR STUDYING THEIR TEXT BOOKS AS PER THE COURSE SYLLABUS

LESSON # 3 (Chapter 2)

Chemistry’s Building Block: The Atom

Life is carried on through chains of chemical reactions

Cells are living things that can respond to their environment. They can move, they can reproduce, and so on. But

How a cell decides to move?

How a cell decides to reproduce?

Cells do what they do as the result of a chain of chemical reactions. In other words, people, plants and animals

function at cellular level due to CHEMISTRY

WHAT IS CHEMISTRY?

Chemistry is the branch of the Science that concerns with matter and its transformations.

Every thing that exists falls into one of two categories: Matter or Energy

WHAT IS MATTER?

MATTER: Is the substance of which physical objects are composed. Matter can be defined as anything that takes up space and has mass. Therefore, mass is a measure of quantity of matter in a given object.

Matter is made of ATOMS

ATOM (from Greek “atomos” meaning indivisible) is the smallest particle still

characterizing a chemical element.

Though “atom” means indivisible, actually atoms are not indivisible. Rather they are composed of

constituents parts:

1- Protons

2- Electrons 3- Neutrons

Subatomic particles

Protons and neutrons are packed tightly together in a core, the atom’s nucleusElectrons move around this core some distance away

2- Electric Charges: Protons: Positively charged Electrons: Negatively charged Neutrons: Have no charge, but are electrically neutral.

The number of protons in an atom ( + charges ) is exactly equal to the number of electrons ( - charges ) .

Therefore, the atom is electrically neutral.

The subatomic particles have mass and electric charge

1- Mass: The mass of the atom resides within the nucleus ( protons and neutrons ). Electrons are negligible with regard to mass

1- THE NATURE OF MATTER IS DEFINED BY THE NUCLEUS: PROTONS AND NEUTRONS

2- THE WAY THAT ELEMENTS COMBINE WITH OTHER ELEMENTS DEPENDS ON ELECTRONS

The number of protons in the nucleus is referred as the ATOMIC NUMBER and defines each element. That is to say, each element has one and only one atomic number.

The atomic number of gold is 79, meaning each atom of gold has ____ protons in its nucleus.

The atomic number of carbon is 6, meaning each carbon atom has ___ protons.

The atomic number of hydrogen is 1, meaning each hydrogen atom has ___ proton in its nucleus.

79

1

6

1- THE NATURE OF MATTER IS DEFINED BY THE NUCLEUS: PROTONS AND NEUTRONS

Nucleus

Generally, in the nucleus the number of protons is equal to the number of neutrons.

CARBON Atomic number 6, meaning 6 protons in the nucleus. In the most common form, Carbon has ____ neutrons.

LEADAtomic number 82, meaning 82 protons in the nucleus. In the most common form, Lead has ____ neutrons

6

82

Exception: HydrogenAtomic number 1, meaning only one proton in the nucleus. The most common form of hydrogen has ___ neutrons. 0

Nucleus

Though usually the number of protons in the nucleus of one specific element is equal to the number of neutrons, in some cases the number of neutrons can be different to the number of protons

When this occurs, the element is still the same element, but now it is called an isotope.

The number of protons and neutrons in one atom is called MASS NUMBERMASS NUMBER = protons + neutronsEx: Carbon has 6 protons and 6 neutrons, therefore the mass number of carbon is _____12

Nucleus

CARBON Atomic number 6, meaning 6 protons in the nucleus. In the most common form, Carbon has 6 neutrons.

p +

n p +

p +

p +

p + p +

n

n

n

n

n

Carbon 12: 6 protons + 6 neutrons

However a relative small amount of carbon exists in a form that has 8 neutrons. The element is still carbon because still has 6 protons (remember that the atomic number define the element).

p +

p +

p + p +

p +

p +

n

n

n

n n

n

Carbon 14: 6 protons + 8 neutrons

n

n

Nucleus

ISOTOPE

Isotopes are heavier than the original element because additional neutrons add weight to the atom. Therefore, isotopes have a different mass number.

p +

p +

p + p +

p +

p +

n

n

n

n n

n p +

p +

p + p +

p +

p +

n

n

n

n n

n n

n

Carbon 14 is heavier than Carbon 12

ISOTOPES are atoms that have the same ATOMIC NUMBER but different MASS NUMBER

Nucleus

I s o t o p e s o f H y d r o g e nNucleus

In most elements, the most common form is that one with the same number of protons and neutrons (ex: carbon 12 is much more abundant than carbon 14). Hydrogen is an exception: the moist abundant is the Hydrogen that has one proton and no neutrons.

Most common form

Imaging the Body with Isotopes

The radioactive isotopes technetium 99 was used in a nuclear medicine scan to provide these images of skeletal portions of the human body.

ISOTOPES are unstable. Unstable atoms are radioactive: their nuclei change or decay by spitting out radiation, in the form of particles or electromagnetic waves, which can be measured by special procedures.Nuclear Medicine is based in that principle.

Nucleus

Positron Emission Tomography (PET scanning) to spot a Brain Tumor

Nucleus

The radiation emitted by radioactive isotopes kills cancer cells, therefore they are used in the treatment of cancer.

1- THE NATURE OF MATTER IS DEFINED BY THE NUCLEUS: PROTONS AND NEUTRONS

2- THE WAY THAT ELEMENTS COMBINE WITH OTHER ELEMENTS DEPENDS ON ELECTRONS

Electrons move around the nucleus in energy levels.

n

n

p + p +

p + p + p + p + p +

p +

n n n

n n

1

Electrons

23

2- THE WAY THAT ELEMENTS COMBINE WITH OTHER ELEMENTS DEPENDS ON ELECTRONS

Each energy level requires a different number of electrons to be filled.

n

n

p + p +

p + p + p + p + p +

p +

n n n

n n

1

-e

-e-e -e

-e

-e

-e -e

-e -e

-e

-e

-e

-e

-e

-e

-e

-e

Argon has atomic number 18Protons: ___ Neutrons: ___ Electrons: ___

181818

Electrons

First level: 2 electrons

Second level: 8 electrons

Third level: 8 electrons

Argon is a stable element because its outermost electron shell is filled

Atoms with the outermost electron shell unfilled are unstable and reactive. Atoms with the outermost electron shell filled are stable and unreactive.

Electrons

Atoms can fill their last level in two ways:

2- By losing or gaining one electron

1- By sharing one or more electrons with another atom

COVALENT BONDING

IONIC BONDING

Atoms attach to one another because they are seeking to fill their outer level or shell

Electrons