GRADE 9 CHEMISTRY REVIEW - MRS. MCINTYRE

GRADE 9 CHEMISTRY REVIEW

THE ATOM

Element: matter composed of only one type of atom. The

periodic table contains all the known elements. Ex: Carbon

(C) ¨C diamonds.

Atom: the smallest particle within an element that retains

the chemical properties of that element. They are

composed of protons, electrons and neutrons.

Protons

Charge

Positive

Electrons

Negative

Neutrons

Neutral

Location

Nucleus

Energy

layers

Nucleus

Mass

1 amu

Negligible

1 amu

Atomic number: the number of protons in an atom.

Ex. The atom drawn above has an atomic number

of 10.

Atomic mass: the number of protons plus the number of

neutrons. An electron mass does not

count because it is so light.

Ex. The mass of the Ne atom above is 10 + 10 = 20

5

11

B

Boron

5 = Atomic number or protons

11 = Atomic mass (p + n)

5 = Number of electrons (it¡¯s neutral) 6 = Neutrons (a.m.- a.n.)

To find the number of particles in an atom:

Protons

Atomic number

Electrons

Same as protons if the atom is neutral

Neutrons

Atomic

number

Atomic

mass

Atomic mass minus atomic number

(protons)

Number to the left of the element in the

periodic table. Indicates the number of

protons.

Number to the right or under the

element in the periodic table. Protons

plus neutrons.

Electrons are separated into energy levels or orbits.

The first energy level has 2 electrons when it is full.

The second energy level has 8 electrons when it is full.

The third energy level has 8 electrons when it is full.

Valence electrons: electrons found in the exterior energy

level of an atom. These are the electrons that create

bonds between atoms.

Ion: an atom with a charge due to gained or lost electrons.

Cation: an atom with a positive charge. It has lost

electrons.

Anion: an atom with a negative charge. It has gained

electrons.

Isotopes: atoms with a different number of neutrons but

the same number of protons. They are the same element

but have a different atomic masses.

PERIODIC TABLE

Families or Groups: vertical columns in the table. All its

elements contain the same number of valence electrons

and share similar properties.

Periods: horizontal rows. They contain the same number

of energy levels.

ELEMENT OR COMPOUND?

CHEMICAL FORMULAS

A chemical formula represents the elements and their quantity in a substance. It is a

standardized way to communicate across languages.

- a subscript on the right of each element is used to indicate the quantity of

that element

- the number one is not used, it is implied by the element symbol

- Remember! An exponent only indicates the charge. Charges are

indicated with a superscript.

Example: CH4

Drawing:

_1__ atom(s) of C

_4__ atom(s) of H

# of bonds: ___4____

Indicate the number of each element in these formulas:

a) MgF2

_1__ atom(s) of Mg

_2__ atom(s) of F

b) Li2S

_2__ atom(s) of Li

_1__ atom(s) of S

c) Sr3Ni2

_3__ atom(s) of Sr

_2__ atom(s) of Ni

d) CuC2H3O2

_1__ atom(s) of Cu

_2__ atom(s) of C

_3__ atom(s) of H

_2__ atom(s) of O

BONDS

A bond is a link between 2 atoms. If the 2 atoms are different elements, another

substance is formed.

For example:

Sodium (a metal) + Chlorine (a gas) ----? Sodium chloride (table salt)

Na

Na

+

Cl

Cl

----?

NaCl

Na

Cl

2 different elements

makes a different

substance

But¡­

H (hydrogen gas) + H (hydrogen gas) ---? H2 (still hydrogen gas)

H

H

H

H

Same elements

together is the same

substance.

A bond forms when electrons are given/taken or shared between 2 atoms.

Atoms want to be stable. An atom is stable when its valence layer is full or empty.

Therefore, atoms will give or take electrons with other atoms to fill/empty the valence

layer.

The noble gases already have a full valence layer so they do not like to form bonds

with other elements. They are already stable.

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