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Atoms

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by

Jim Davidson

on 21 October 2014

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Transcript of Atoms

Atoms
These are the smallest building blocks of elements.
The nucleus contains positive protons and neutral neutrons

The electrons orbit around in shells and are negatively charged
The nucleus contains positive protons and neutral neutrons

The electrons orbit around in shells and are negatively charged
Atoms
Ionic Bonding
Bonds formed when a metal and a non-metal react
Defined as a
transfer of
electrons
The metals always
lose electrons to become positive ions

The non-metals always gain electrons to
become negative ions
Ionic bonds are held
together by an electrostatic attraction
The alternating charges are held
together in a regular pattern called an ionic lattice.

This can be used to explain the properties of ionic compounds
Properties of Ionic compound
Very high mpt/bpt - many electrostatic forces to overcome

Conduct electricity when molten/dissolved - ions can move

Electrical insulators when solid - ions cannot move

Easiliy dissolve in water
Covalent Bonding
Bonds formed when electrons are shared

Usually formed between two non-metals
Covalent Bonds
Defined as a
shared pair
of electrons
These can be shown as dot and cross diagrams like the one above

The bonds can be single (one shared pair), double (two shared pairs) or triple (3 shared pairs)

Low mpt/bpt - very small molecules with weak intermolecular forces
Electrical insulators - electrons cannot move freely
Usually insoluble in water
Giant Covalent Molecules
Very high melting point - many bonds to overcome
Usually very hard

Examples:
Silicon dioxide (sand)
Diamond
Graphite
Metals
Properties:

High mpt/bpt - large metallic lattice

Conduct electricity - delocalised electrons can
move freely

Insoluble in water

Malleable & Ductile - atoms can easily slide across each other when force is applied
C2
Group 1 - Alkali Metals
Trends:

Bpt/mpt decrease as you go down the group

Reactivity increases as you go down the group - outer electron further away from nucleus
extra shielding of nucleus by more electrons

Softer as you go down group
Reactions
Water:

2Li + 2H2O -------> 2LiOH + H2


Halogens:

2Li + F2 -------> 2LiF
The Halogens - Group 7
Fluorine
- Most reactive - Gas - Low
bpt

Chlorine
- Gas

Bromine
- Liquid

Iodine
- Solid
Properties
Diatomic - Have to form molecules of 2 atoms

React with group 1 metals to make salts

React with water to make various acids

Can undergo displacement reactions - the more reactive halogen will displace less reactive halogens

This is evidenced by a colour change - you see the colour of the displaced halogen
Noble Gases
Called so because they are very unreactive - stability due to full outer electron shell

Used to fill light bulbs, welding and airships because they will not react

Bpt and density increase as you go down the group - the atoms are getting bigger

Bpt and density of any noble gas will be about midway between the noble gases above and below it in the group
Rates of Reaction
Factors that affect rate:

Temperature
Concentration of reactants
Surface area
Use of a catalyst
Collision Theory
Particles must collide to react

Not all collisions result in a reaction

Only collisions above the activation energy cause a reaction

The rate of reaction depends on the number of succesful collisions in a unit of time
When temperature increases, the speed of the reacting particles increases.

This means they collide more often, and with more force, in the same amount of time.

This increases the number of effective collisions in the same amount of time.
This increases the number of reacting particles.

This means that there are more particles colliding in the same amount of time.
Increasing surface area increases the number of collisions in the same amount of time.


REMEMBER:

The smaller the solid particles are the LARGER
Full transcript