8 th Grade Science. Atomic Structure Atoms have a nucleus that contains Protons and Neutrons Electrons are contained in shells that surround the nucleus.

8th Grade Science

Atomic Structure

• Atoms have a nucleus that contains Protons and Neutrons

• Electrons are contained in shells that surround the nucleus

• An atom is made of mostly empty space

• Protons have a positive charge

• Electrons have a negative charge

• Neutrons are Neutral

Valence Electrons

• Each electron shell can hold a certain number of electrons

• Electron shells are filled from the inside out

• Noble Gases have full outer electron shells

• All other elements have partially filled outer electron shells

Electron Shell Number of Electrons

1 2

2 8

3 8

4 18

5 18

6 32

7 32

Valence Electrons

• The electrons in the outer most electron shell are called valence electrons

• The shell containing electrons that is furthest from the nucleus is called the valence shell

• The number of electron shells with electrons is the same as the period number

Noble Gas Stability

• Noble gases are usually unreactive• This is because they have full valence

shells• An element with a full valence shell is a

happy element • For two atoms to join together atoms must

gain, lose or share electrons• Elements with full valence shells do not

easily gain or lose electrons

Noble Gas Stability

• Atoms want to gain stability

• Atoms will try to gain or lose electrons to have a full valence shell

• Metals try to lose electrons

• Non-Metals try to gain electrons

Becoming An Ion

• Electrons are negatively charged

• Protons are positively charged

• Neutral atoms do not have a charge because the number of protons is the same as the number of electrons

• When atoms gain or lose electrons they become positively or negatively charged

• An atom with a charge is called an Ion

In covalent bonding,atoms still want to achievea noble gas configuration(the octet rule).

But rather than losing or gainingelectrons,atoms now share an electron pair.

Covalent & Ionic Bonds

LET’SFIRSTREVIEWIONICBONDING

In an IONIC bond,electrons are lost or gained,resulting in the formation of IONS

in ionic compounds.

FK

FK

FK

FK

FK

FK+ _

FK+ _

The compound potassium fluorideconsists of potassium (K+) ions

and fluoride (F-) ions

FK+ _

The ionic bond is the attractionbetween the positive K+ ion

and the negative F- ion

Covalent Bonds

Sowhatarecovalentbonds?

In covalent bonding,atoms still want to achievea noble gas configuration(the octet rule).

In covalent bonding,atoms still want to achievea noble gas configuration(the octet rule).

But rather than losing or gainingelectrons,atoms now share an electron pair.

In covalent bonding,atoms still want to achievea noble gas configuration(the octet rule).

But rather than losing or gainingelectrons,atoms now share an electron pair.

The shared electron pairis called a bonding pair

Cl2

Chlorineforms

acovalent

bondwithitself

ClClHowwilltwochlorineatomsreact?

ClClEach chlorine atom wants to gain one electron to achieve an octet

ClClNeither atom will give up an electron –chlorine is highly electronegative.

What’s the solution – what can theydo to achieve an octet?

ClCl

Cl Cl

Cl Cl

Cl Cl

Cl Cloctet

Cl Cl

circle the electrons foreach atom that completestheir octets

octet

Cl Cl

circle the electrons foreach atom that completestheir octets

The octet is achieved byeach atom sharing theelectron pair in the middle

Cl Cl

circle the electrons foreach atom that completestheir octets

The octet is achieved byeach atom sharing theelectron pair in the middle

Cl Cl

circle the electrons foreach atom that completestheir octets

This is the bonding pair

Cl Cl

circle the electrons foreach atom that completestheir octets

It is a single bonding pair

Cl Cl

circle the electrons foreach atom that completestheir octets

It is called a SINGLE BOND

Cl Cl

circle the electrons foreach atom that completestheir octets

Single bonds are abbreviatedwith a dash

Cl Cl

circle the electrons foreach atom that completestheir octets

This is the chlorine molecule,

Cl2

O2

Oxygen is also one of the diatomic molecules

How will two oxygen atoms bond?

OO

OOEach atom has two unpaired electrons

OO

OO

OO

OO

OO

OO

Oxygen atoms are highly electronegative.

So both atoms want to gain two electrons.

OO

Oxygen atoms are highly electronegative.

So both atoms want to gain two electrons.

OO

OO

OO

OO

OO

OOBoth electron pairs are shared.

6 valence electronsplus 2 shared electrons

= full octet

OO

6 valence electronsplus 2 shared electrons

= full octet

OO

two bonding pairs,

OOmaking a double bond

OO=For convenience, the double bond

can be shown as two dashes.

OO

OO=This is the oxygen molecule,

O2

this is so

cool!!

Answer these questions:

An atom that gains one or more electrons will have a ____________________ charge.

An atom that loses one or more electrons will have a ____________________ charge.

An atom that gains or loses one or more electrons is called an ____________.

A positive ion is called a ______________ and a negative ion is called an _______________.

POSITIVE

NEGATIVE

ION

CATIONANION

“An-Eye-On”“Cat-Eye-On”

What is an ionic bond?

Atoms will transfer one or more ________________ to another to form the bond.

Each atom is left with a ________________ outer shell.

An ionic bond forms between a ___________ ion with a positive charge and a ________________ ion with a negative charge.

Example B1: Sodium + Chlorine Example B2: Magnesium + Iodine

ELECTRONS

COMPLETE

METALNONMETAL

What is a covalent bond?

Atoms ___________ one or more electrons with each other to form the bond.

Each atom is left with a ________________ outer shell.

A covalent bond forms between two _________________.

Example C1: Hydrogen + Hydrogen Example C2: 2 Hydrogen + Oxygen

SHARE

COMPLETE

NONMETAL