SCIENCE - Periodic Table, Elements and Bonding

Atom

The smallest part of an element, which still has the properties of that element. Everything is made of atoms. No one has ever seen an atom.

Element

Contains one type of atom. It is the simplest form of a substance. Each element is given a unique symbol, e.g. O for Oxygen

Molecule

When 2 or more atoms join together chemically (bonded), e.g. O_2,

Compound

It forms when two different elements chemically combine, e.g. H2O

What is air made of?

A mixture of molecules and compounds

What is the atom made of?

• Protons (+)

• Neutrons

• Electrons (-)

Where are Protons and Neutrons found?

The nucleus

What do electrons do?

They spin around the nucleus

What are Protons, Neutrons and Electrons known as?

Subatomic particles

Proton Mass

1

Neutron Mass

1

Electron Mass

0 - It would take 2000 electrons to weigh the same as a proton

Atomic Number

The number of protons in the nucleus of that element

Number of Protons = Number of Electrons

True or False: Elements are completely neutral

True

Mass Number

The number of protons and neutrons in the nucleus of the atom

How do you find the amount of Neutrons?

Mass Number - Atomic Number = Number of Neutrons

What model is typically used to show an atom?

The Bohr Model

Electron Configuration

How you display electrons in an atom

Electron Configuration Rules for Bohr Model

• Fill from inside to outside

• First orbit - Up to 2 electrons

• Second orbit - Up to 8 electrons

• Third orbit - Up to 8 electrons

Periodic Table

A list of all known elements (118) created by Demitri Mendeleev

Vertical Columns

• Called Groups

• They have elements that have similar physical and chemical properties

Horizontal Rows

• Called Periods

• They are in order of increasing proton number

Group Names

Group 1 - The Alkali Metals

Group 2 - The Alkali Earth Metals

Group 7 - The Halogens

Group 8 - The Noble Gasses

Group 1

THE ALKALI METALS:

• They have 1 electron in their outer shell - They want to get rid of this electron

• This group is very reactive - Can even react with the air - Increasing reactivity as you move down the group

• Very soft - can be cut with a knife

• Form +1 ions

Group 2

THE ALKALINE EARTH METALS:

• 2 electrons in outer shell

• Reactive - not as much as Group 1

• Harder than Group 1

• Form +2 ions

Group 7

THE HALOGENS:

• 7 electrons in outer shell - need to gain one to have a full shell

• Highly reactive

• Form -1 ions

Group 8

THE NOBLE GASSES:

• All gasses

• Full shell of outer electrons

• Very unreactive - Stable

• Do not form ions

Full Outer shell =

Stability

Group Number Electron Correlation

The group number correlates with the number of electrons in the atom’s outer shell

Chemical Bonding

Two types:

Ionic and Covalent

Ionic Bonding

When one atom loses electrons and another atom gains electrons.

An ionic bond is the force of attraction between oppositely charged ions in a compound

Where does Ionic bonding occur?

Between metals and non-metals

Examples of Ionic Bonding

NaCl (Sodium Chloride)

Sodium Ion

• Sodium has only one electron in it’s outer shell

• It needs to lose the electron

• If it loses one electron, it will become positive as there are more protons than electrons

• After losing an electron, sodium becomes an ion and is represented like [Na]⁺

Atom that has lost electrons

Cation (+)

Atom that has gained electrons

Anion (-)

Why do Ions attract each other?

They attract each other because the have charges. Opposite charges make this bond very strong.

Ionic Bonding Properties

• Most ionically bonded substances are solids at room temp.

• Most have high melting points because they are so strong

• Because the ions have their own charge, they conduct electricity

• They are soluble in water

Covalent Bonding

Covalent bonds allow atoms to share electrons so that they can get a full outer shell

• It is a strong bond made up of a shared pair of electrons between two atoms

Where does Covalent Bonding occur

Between non-metal atoms

Simplest Covalent Bond

Hydrogen (H2)

Covalent Bonding examples

H2O Water

CH4 Methane

Cl2 Chlorine

Methane

CH4

• Carbon wants to gain 4 electrons

• Hydrogen wants to gain 1 electron

• One carbon can bond and share electrons with four hydrogens

Chemical Formulas

Every compound has a formula. It tells you the type and number of atoms present. Made up of letters which denote the type of atom and numbers which tell how much of that atom is there, e.g. CH4 = 1 carbon 4 hydrogen

Combining Metals and Non-Metals (naming)

When metals and non-metals are combined they are named as follows:

Metal + Non-metal + ide

Examples: Sodium + Chlorine = Sodium Chloride

Combining Metals, Non-metals and Oxygen (naming)

When metals, non-metals and oxygen are combined they are named as follows:

Metal + Non-metal + ate

Example: Potassium + Phosphorous + Oxygen = Potassium Phosphate

Combining Metals and Non-metals

We need to work out the combining power of an atom to combine it (This means how many electrons does the atom need to become stable and non-reactive)

Example:

Hydrogen - Group 1 - Needs 1 more electron to be stable - Combining power = 1

Carbon - Group 4 - Needs 4 more electrons to be stable - Combining power = 4

It would take 4 hydrogen atoms to every 1 carbon atom to keep both atoms stable

CH4 is formed

Which 3 elements is the Octet rule not true for

Hydrogen, Berylium and Boron

Outer shell also known as

Valence shell