Bonding 4thJuly2015

8/17/2019 Bonding 4thJuly2015

1/33

Covalent Bonding

4th July 2015

Secondary 3 Chemistry


2/33

Helium

atom

An atomic model


3/33

What are Electron Shells?

a) Atomic number = number of Electrons

b) Electrons vary in the amount of energy they

possess, and they occur at certain energy levels

or electron shells.

c) Electron shells determine how an atom

behaves when it encounters other atoms


4/33

Octet Rule = atoms tend to gain, lose or share electrons soas to have 8 electrons

C would like to

N would like to

O would like to

Gain 4 electrons

Gain 3 electronsGain 2 electrons


5/33


6/33

Electron Dot Structures

Symbols of atoms with dots to represent the valence-shell

electrons

1 2 3 4 5 6 7 8

H He:

Li Be B C N O : F :Ne :

Na Mg Al Si P S :Cl :Ar:


7/33

Learning Check

A. X would be the electron dot formula for

1) Na 2) K 3) Al

B. X would be the electron dot formula

1) B 2) N 3) P


8/33

Covalent Bonding

• Chemical bonds involve the sharing ofelectrons to form a covalent bond.

• An atom is the smallest unit of matter thatcontains electrons.

• The number of electrons an atom has,determines the number of bonds the atom

can have.


9/33

Covalent Bonding

• Is between atoms of non-metals.

•

Covalent bonding occurs in non-metalliccompounds like methane, hydrogen chloride

and water!


10/33

Cl2

Chlorine

formsa

covalent

bondwith

itself


11/33

ClCl

How will the 2 chlorine atoms react?

Answer: Each chlorine atom wants to gain

one electron to achieve an octet


12/33

Cl Cl

Cl Cl

octet

Cl Cl

octet


13/33

The octet is achieved by each atom sharing the electron

pair in the middle.

Cl Cl

Cl ClSingle bonds are abbreviated with a dash


14/33

How will two oxygen atoms bond?OO

OOEach atom has two unpaired electrons.


15/33

Oxygen atoms are highly electronegative.

So both atoms want to gain two electrons.

OO


16/33

OO

OOBoth electron pairs are shared.Two pairs of electrons make two bonds


17/33

OO

6 valence electrons

plus 2 shared electrons

= full octet

OO=For convenience, the double bond

can be shown as two dashes.


18/33

- water is a polar molecule because oxygen is more

electronegative than hydrogen, and therefore electrons

are pulled closer to oxygen.


19/33

Formation of Ions from Metals –

Ionic Compounds

Ionic compounds result when metals react withnonmetals

Metals lose electrons to match the number of valence

electrons of their nearest noble gas

Positive ions form when the number of electrons are

less than the number of protons

Group 1 metals ion 1+




20/33

Formation of Sodium Ion

Sodium atom Sodium ion

Na – e Na +

2-8-1 2-8 ( = Ne)

11 p

+

11 p

+

11 e- 10 e-

0 1+


21/33

Formation of Magnesium Ion

Magnesium atom Magnesium ion

Mg – 2e Mg2+

2-8-2 2-8 (=Ne)

12 p+ 12 p+12 e- 10 e-

0 2+


22/33


23/33

Learning Check

A. Number of valence electrons in aluminum

1) 1 e- 2) 2 e- 3) 3 e-

B. Change in electrons for octet

1) lose 3e- 2) gain 3 e- 3) gain 5 e-

C.Ionic charge of aluminum

1) 3- 2) 5- 3) 3+


24/33

Solution

A. Number of valence electrons in aluminum

3) 3 e-

B. Change in electrons for octet

1) lose 3e-

C.Ionic charge of aluminum

3) 3+


25/33

Learning Check

Give the ionic charge for each of the following:

A. 12 p+ and 10 e-

1) 0 2) 2+ 3) 2-

B. 50p+ and 46 e-

1) 2+ 2) 4+ 3) 4-

C. 15 p+ and 18e-

2) 3+ 2) 3- 3) 5-


26/33

Ions from Nonmetal Ions

In ionic compounds, nonmetals with atomic

number of 15, 16, and 17 gain electrons from

metals

Nonmetal add electrons to achieve the octet

arrangement

Nonmetal ionic charge:

3-, 2-, or 1-


27/33

Fluoride Ion

unpaired electron octet

1 -

: F + e : F :

2-7 2-8 (= Ne)

9 p+ 9 p+

9 e- 10 e-

0 1 -

ionic charge


28/33

In an IONIC bond,

electrons are lost or gained,

resulting in the formation of IONS

in ionic compounds.

FK


29/33

FK + _

The compound potassium fluoride

consists of potassium (K +) ions

and fluoride (F-) ions


30/33

1). Ionic bond –

electron from Na is transferred to Cl,this causes a charge imbalance in each atom. The Na

becomes (Na+) and the Cl becomes (Cl-), charged

particles or ions.


31/33

Metallic Bond

• Formed between atoms of metallic elements

• Holds metal atoms together very strongly.

• Electron cloud around atoms

• Good conductors at all states, lustrous, very high

melting points

• Examples; Na, Fe, Al, Au, Co


32/33

Ionic Bond, A Sea of Electrons


33/33

Metals Form Alloys

Metals do not combine with metals. They form

Alloys which is a solution of a metal in a metal.

Examples are steel, brass, bronze and pewter.

Bonding 4thJuly2015

Documents

Transcript of Bonding 4thJuly2015