4.1 Atomic Theory & Bonding

ATOM: smallest particle of an element, has a neutral charge.

PEN = proton(s) + electron(s) + neutron(s)

ELEMENT: made up of 1 type of atom (eg.oxygen O)

IONS: atoms with charges (eg. oxygen is O2-)

MOLECULES: groups of covalently bonded atoms (eg. oxygen molecules are O2)

COMPOUNDS: are made up of at least 2 atoms bonded together.

Hydrogen and oxygen are atoms/elements

H2O is a compound

Structure of an Atom:

Name Symbol Charg

e Location

Atomic

Mass

Proton p 1+ nucleus 1 AMU

Neutron n 0 nucleus 1 AMU

Electron e 1– area surrounding

the nucleus 1/1836 (0)

Numbers to Remember :

Protons = Atomic Number

Neutrons = Mass number – Atomic number (Mass # - proton #).

Neutrons + Protons = Mass #

Electrons in an atom = atomic number (also proton #)

Electrons in an ion = atomic number – ion charge

Families of the Periodic Table:

Columns of elements are called groups, or families

All elements in a family have…

similar properties

bond with other elements in similar ways

have the same number of valence electrons

Family names (on the periodic table!):

Group 1 = alkali metals (1+, highly reactive)

Group 2 = alkaline earth metals (2+, reactive)

Group 17 = the halogens (1-, very reactive)

Group 18 = noble gases (0, unreactive)

Periods are horizontal rows on the periodic table.

INC

RE

AS

ING

RE

AC

TIV

ITY

Where are the

following?

• Atomic

Number

• Period

• Group/Family

• Metals

• Non-metals

• Transition

metals

• Metalloids

• Alkali metals

• Alkaline earth

metals

• Halogens

• Noble gases

Periodic Table & Ion Formation:

Ions: Atoms that gain and lose electrons to become

stable (full valence shells).

1. Cations: metals that lose electrons & form

positive ions (Na+)

Multivalent: Some metals can have more than

one charge (Fe2+ or Fe3+).

2. Anions: Non-metals gain electrons & form

negative ions (O-2)

Bohr Diagrams:

Bohr diagrams show how many electrons

appear in each electron shell around an

atom. (2, 8, 8, 18, 18)

Valence electrons: electrons in the outermost

shell ONLY.

If the valence shell is full = stable

If the valence shell is not full = reactive

What element is this?

Bohr Diagrams

•It has 2 + 8 + 8 = 18

electrons, and therefore

18 protons

•It has 8 electrons in the

outer (valence) shell

18 p

22 n

Argon!

Ionic Bonds:

Formed between Metals (cations) & non-metals (anions).

Valence electrons are transferred from metal to nonmetal.

Eg. Li2O

Lithium Oxygen

+

Electrons are transferred from

the cations to the anion Li+ O2- Li+

Lithium oxide,

Li2O

Formed between two or more non-metals

Valence electrons are shared between atoms

Eg. HF

Covalent Bonds:

Hydrogen Fluorine

+

Electrons are shared

Hydrogen fluoride

Lewis Diagrams:

Only valence electrons are shown

Dots representing valence electrons are placed around the element symbols (on 4 sides, imagine a box around the symbol)

Electron dots are placed singularly,

then they are paired.

Ex: Nitrogen

atom

Lewis Diagrams for Ions:

Ex. Nitrogen ion

Remove or add electron dots to

make full valence shells.

Square brackets and the charge

are placed around each ion

Be Cl

• •

• •

• •

• •

Each beryllium has two

electrons to transfer

away, and each chlorine

wants one more electron

Be Cl Cl • •

• •

• •

• •

• •

• •

• •

• •

• •

• •

• •

• •

Be Cl Cl • •

• •

• •

• •

• •

• •

• •

• •

• •

• •

• •

• •

Since Be2+ wants to

donate 2 electrons and

each Cl– wants to

accept only one, two Cl–

ions are necessary

The ionic compound

Beryllium chloride is

formed

2+ – • •

• •

• •

• •

–

Lewis Diagrams For Covalent Bonds:

valence electrons are drawn to show sharing of electrons.

Remember: All atoms “like” to have a full valence shell

The shared pairs (“bonding pairs”) of electrons are usually drawn as a straight line

“lone pairs” are the electrons not shared