Science and Tech 11
1.
An atom is the smallest particle of an
element that has the properties of that
element.
2.
An element is a pure substance that cannot
be chemically broken down into simpler
substances.
Example: Oxygen (O) is an element.
3.
A compound is a pure
substance that is made up of
two or more different elements
that have been combined in a
specific way.
4.
Example: H2O is a compound
made of the elements hydrogen
and oxygen.
4.
An atom includes smaller particles called
protons, neutrons, and electrons:

Protons are subatomic particles that have a
1+ (positive) charge.

Neutrons are subatomic particles that do
not have an electric charge.

Electrons are subatomic particles that have
a 1− (negative) electric charge.

The nucleus is:
 at the centre of an atom
 composed of
protons and neutrons.

Electrons exist in the area
surrounding the nucleus.
The atomic number
= the # of protons = the # of electrons

the # of protons in the nucleus determine the
element.
For example,
silver (Ag) has 47 protons

The periodic table organizes all known
elements in order by atomic number.

Rows of elements (across) are called periods.
Columns of elements (down) are called
chemical families or groups.

COLUMNS= GROUPS
ROWS = PERIODS
 All elements in a family have similar properties and





bond with other elements in similar ways.
Group 1 = alkali metals
Group 2 = alkaline earth metals
Group 17 = halogens
Group 18 = noble gases
Metals are on the left side of the table, nonmetals are on the right side, and the metalloids
form a “staircase” toward the right side.
Atoms gain and lose
1.
electrons to form bonds.

When atoms gain or lose
electrons, they become
electrically charged
particles called ions.
2.
Metals lose electrons and
become positive ions (aka
“cation”).
 Some metals are multivalent,
which means they lose electrons
in different ways
 Iron (Fe) loses either 2 electrons
(Fe2+) or 3 electrons (Fe3+) as
shown in the periodic table.
3.
Non-metals gain
electrons and
become negative
ions (aka
‘anions’).

A Bohr diagram is a model of the atom that
describes the arrangement of an element’s
subatomic particles.

Electron shells are regular patterns or energy
levels around the nucleus.

There is a maximum of 2 electrons in the 1st
shell, 8 electrons in the 2nd shell, and 8
electrons in the 3rd shell.

Electrons in the outermost shell are called
valence electrons.
2.
Patterns seen in the Periodic Table of Elements:
 By PERIOD:
▪ The period number equals the # of shells in the atom.
 By GROUPS:
▪ Except for the transition elements (Groups 3–12), the last digit
of the group number equals the number of electrons in the
valence shell.
Example:
Period 2 elements have only 2 shells (or energy levels)
1
2
3
4
5
6
7
Example:
Group 1 = 1 valence
electron
Group 13 = 3 valence
electrons
3.
A full valence shell is very stable
and atoms will lose or gain
electrons to accomplish this
 Why atoms may bond or react with
other atoms
 The noble gas elements already have
full electron shells and are very stable
and thus, rarely react with other
elements
4.
Electrons can exist
singly as unpaired
electrons, or they
can be in pairs, called
paired electrons.
Science and Tech 11

Atoms want to achieve a
full valence shell and will
lose or gain electrons to
do this.
 very stable and have low
energy states (ie: noble
gases)

Cations are:
 an atom of metal that loses
electrons to other atoms

Anions are:
 an atom of non-metal that gains
electrons from other atoms

Atoms can also share electrons

There are two ways that ions
can form compounds:
1. IONIC BONDING
(IONIC COMPOUNDS)
2. COVALENT BONDING
(COVALENT COMPOUNDS)

Ionic compounds are formed usually between a
METAL/CATION and a NON-METAL/ANION

one or more electrons are transferred from the
metal to the non-metal
Example #1:
Sodium (Na) is a metal that can get a full valence shell by losing 1
electron and chlorine (Cl) is a non-metal that can get a full valence
shell by gaining 1 electron. They’re perfect for each other and they
form sodium chloride (NaCl)!
Example #2:
Calcium fluoride (CaF2) is an ionic compounds formed
from 1 atom of the metal calcium and 2 atoms of the nonmetal fluorine. The calcium atom transfers 2 electrons in
total (1 electron to each of the fluorine atoms).

covalent compounds/molecules are formed
when two non-metal atoms share electrons
(“CO” = together/share and “VALENT” = valence
electrons  shared valence electrons)


the term ‘molecule’ applies specifically to
covalent compounds
some common covalent compounds are
water, methane, ammonia, and carbon
dioxide

Bonding pair:
 Each atom in a covalent molecule will share 1
valence electron
 Any pairs of valence electrons NOT shared are
called lone pairs.

Some elements are more stable when paired
as two atoms that share electrons. These
molecules are called diatomic molecules.

Elements that are diatomic are: hydrogen (H2),
nitrogen (N2), oxygen (O2), chlorine (Cl2), fluorine
(F2), bromine (Br2), and iodine (I2).

Lewis diagrams are great for illustrating
chemical bonding because they show only
the valence electrons of atoms
 A lot less work than drawing Bohr diagrams!
Ca
1.
figure out how many valence
electrons an atom has
2.
place 1 electron at a time
starting at the North position
until all electrons have been
place

you may end up with paired and
unpaired electrons
1.
find the electric charge of the element
2.
the cation will have no valence electrons and
the anion will have a full valance shell
3.
add square brackets around each atom
4.
include an ion charge to the top right
Example: Sodium chloride (NaCl)
Example: Barium bromide (BaBr2)
1.
identify bonding pair (shared electrons)
2.
draw a line to represent the bonding pair
Example: water (H2O)
Example: Methane (CH4)