Chemistry ReviewAtomic Theory

Science and Tech 11

ATOMIC THEORY

1. An atom is the smallest particle of an element that has the properties of that element.

ATOMIC THEORY

2. An element is a pure substance that cannot be chemically broken down into simpler substances. Example: Oxygen (O) is an element.

ATOMIC THEORY

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.

ATOMIC THEORY

4. An atom includes smaller particles called protons, neutrons, and electrons:

ATOMIC THEORY

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

The nucleus is: at the centre of an

atom composed of

protons and neutrons.

Electrons exist in the area surrounding the nucleus.

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 OF ELEMENTS

THE PERIODIC TABLE OF ELEMENTS

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.

ROWS = PERIODS

CO

LU

MN

S=

G

RO

UP

S

THE PERIODIC TABLE OF ELEMENTS

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, non-metals are on the right side, and the metalloids form a “staircase” toward the right side.

ION FORMATION

1. Atoms gain and lose

electrons to form

bonds.

When atoms gain or lose

electrons, they become

electrically charged

particles called ions.

ION FORMATION

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.

ION FORMATION

3. Non-metals gain electrons and become negative ions (aka ‘anions’).

BOHR DIAGRAMS

A Bohr diagram is a model of the atom that describes the arrangement of an element’s subatomic particles.

BOHR DIAGRAMS

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.

BOHR DIAGRAMs

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)1234567

Example:Group 1 = 1

valence electron

Group 13 = 3 valence electrons

BOHR DIAGRAMs

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

BOHR DIAGRAMS

4. Electrons can exist singly as unpaired electrons, or they can be in pairs, called paired electrons.

Chemistry Review (part 2):Forming Compounds

Science and Tech 11

Background:

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)

Background:

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

Background:

Atoms can also share electrons

Background:

There are two ways that ions can form compounds:1. IONIC BONDING

(IONIC COMPOUNDS)

2. COVALENT BONDING (COVALENT COMPOUNDS)

IONIC 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 non-metal fluorine. The calcium atom transfers 2 electrons in total (1 electron to each of the fluorine atoms).

COVALENT COMPOUNDS

covalent compounds/molecules are formed when two non-metal atoms share electrons

(“CO” = together/share and “VALENT” = valence electrons shared valence electrons)

COVALENT COMPOUNDS

the term ‘molecule’ applies specifically to covalent compounds

some common covalent compounds are water, methane, ammonia, and carbon dioxide

COVALENT COMPOUNDS

Bonding pair: Each atom in a covalent molecule will

share 1 valence electron Any pairs of valence electrons NOT

shared are called lone pairs.

COVALENT COMPOUNDS

Some elements are more stable when paired as two atoms that share electrons. These molecules are called diatomic molecules.

COVALENT COMPOUNDS

Elements that are diatomic are: hydrogen

(H2), nitrogen (N2), oxygen (O2), chlorine

(Cl2), fluorine (F2), bromine (Br2), and

iodine (I2).

LEWIS DIAGRAMS

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

To draw a Lewis diagram, follow these steps:

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

To draw a Lewis diagram to illustrate ionic bonding:

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)

To draw a Lewis diagram to illustrate covalent bonding:

1. identify bonding pair (shared electrons)

2. draw a line to represent the bonding pair

Example: water (H2O) Example: Methane (CH4)

EXIT SLIP!!