chemistry 2 lesson 1.5 covalent bonding aqa additional science
TRANSCRIPT
Aims
Class workCovalent Bonds
LO’s• What are covalent bonds?
Write it down!! Page 45© C Meyer
All• Know what a covalent bond is• Know covalent bonds can be
either small or large moleculesMost• Draw dot and cross diagrams for
covalent bondSome• Draw dot and cross diagrams for
complex molecules
Aims
Following the previously shown slides draw bonding diagrams for the compounds formed from the following atoms:
1. Lithium (2.1) and fluorine (2.7)2. Magnesium (2.8.2) and chlorine (2.8.7)3. Aluminium (2.8.3) and fluorine (2.7)
Remember that the total number of electrons lost by the metal must equal the total number of electrons gained by
the non-metal
Homework
Sodium Fluoride
Sodium atom Fluorineatom
Copy the diagram and draw another box showing the electron configuration in sodium fluoride.
2.82.8
FNa
2.8.1. 2.7
Na+ F-
+ -
Bonding in Aluminium Fluoride
In aluminium fluoride it is the non-metal atoms that we need more of.
F
F
F
Al Al
F
F
F
Brackets??
COVALENT BONDING
Hydrogen chloride
molecule
HClCount the electrons in the outer shell of
each atom. Are they full?Click
Cl
What is differentto ionic bonding??
H
Cl17
H1
What are covalent bonds?Info
Box
m1
Now lets look at a more complicated molecule
MethaneMethane
Click
Methane (found in natural gas)
CH4
Info
Box
H1
C6
C
H
m1
Title - Covalent compounds
• Formed when non-metal atoms react together.
• Atoms share outer shell electrons.• Shared electrons count towards
filling shells of both atoms to make full 2, 8, 8 pattern.
What are covalent bonds?
m3
You need to know different ways to show covalent bonds:-
• A pair of electrons shared like this is a covalent bondcovalent bond..
• Shown in full bonding diagrams (see figure 1). Or just shown as a pair of electrons (xx) or even just a line (see figure 2).
m4
FX
X F FF-Figure 1 Figure 2
Ways to show covalent bonds
What are covalent bonds?
Small covalent structures
• Can be simple!• Sometimes just a few atoms join together in
this way. • This produces small covalent molecules –
often known as simple molecular structures.
a simple molecularstructure
covalent bonds
Giant covalent structures
• Can be complex!!• Sometimes millions of atoms are
joined together by covalent bonds. • This produces a rigid 3-D network
called a giant latticegiant lattice..
a giant lattice
covalent bonds
Covalent bonding and electron structures
• Covalent bonding wants outer electron shells that are completely full.
• Done by sharing electrons where shared electrons are in outer shells of both atoms.
• Can be done with more than 2 atoms
Cl Cl C
H
H H
H
N
H
HH Cl H
Covalent bonding in chlorine
Chlorine (2.8.7) needs 1 more electron to attain a full electron shell.
Cl
(2,8,7)
Cl
(2,8,7)
Cl
(2,8,8)
Cl
(2,8,8)
Draw it!Cl-Cl
Covalent bonding in hydrogen chloride
Both hydrogen (1) and chlorine (2.8.7) needs 1 more electron to attain a full outer shell. Another example
H
(2)
Cl
(2,8,8)
H-ClCl
(2,8,7)
H
(1)
Electronic structure of H and Cl??
Electronic structure of HCl??
m2
Covalent bonding in water
What are we going to do with water??Hydrogen (1) needs 1 more electron but oxygen (2.6) needs 2 more.
O H
H
O H
H
O
H
H
Electronic structure of H and O??
• Hydrogen (1) needs 1 more electron.
• How many does nitrogen (2.5) need?
• How many hydrogens per 1 nitrogen?
• Draw bonding diagrams for ammonia.
N H
H
HN H
H
H
3
3
• Hydrogen (1) needs 1 more electron.
• How many does carbon (2.4) need to make 8?
• How many hydrogens per 1 carbon?
• Draw bonding diagrams for methane.
4
4
C H
H
H
H
C H
H
H
H
How could we draw this with lines?
Covalent bonding - multiple bonds
• Mostly electrons are shared as pairs.• In some compounds they are shared in
fours or even sixes.• This gives rise to double and triple
covalent bonds.• Again, each pair of electrons is often
represented by a single line when doing simple diagrams of molecules.
Cl-ClSingle bond
O=ODouble bond
N=NTriple bond
Covalent bonding in oxygen
Oxygen (2.8.6) needs 2 more electrons to attain a full electron shell.
OO O=O
OO
4 electrons
Nitrogen (2.8.5) needs 3 more electrons to attain a full electron shell and forms a triple bond.Draw a bonding diagram of nitrogen.
6 electrons
NN
N N
N=N
Giant covalent structures: diamond
• One form of carbon is diamond.
• Each diamond consists of millions of carbon atoms bonded into a single giant structure.
• It is veryvery hard.
Diamondstrong
covalentbonds
carbon atoms
Giant covalent structures: sand
• Sand is an impure form of silicon dioxide.
• Although it is a compound, it has a giant covalent structure with certain similarities to diamond.
silicon atoms
oxygen atoms
Ionic or covalent bonds??1. Methane2. Sodium Chloride3. Oxygen4. Water5. Magnesium Oxide6. Carbon7. Calcium Chloride8. Explain covalent bonding
What have I learnt?
What have I learnt?
The End