Atomic structure

What is an atom?

• the smallest pieces of an element that can exist

What are compounds?

• atoms of different elements that are combined together

What are the key features of a chemcial reaction?

• compounds are broken up or formed

• at least 1 new substance is created

• measurable energy change

• no atoms created or destroyed

What are mixtures?

• made of 2 or more substances (elements or compounds) that haven’t been chemically combined

• so they can be seperated

• e.g air is a mixture

What are the different seperation techniques for mixtures?

• Filtration

• Crystallisation

• Chromotography

What’s filtration?

• seperates mixtures of insoluble solids and liquids

• done by puring the mixture through filter paper: insoluble solid is trapped, the liquid runs through the paper and is collected

What’s crystallisation?

• seperates solutions into their constituent parts: dissolved solids and liquids

• heat the mixture so that the solvent evaporates

• eventually, crystals of the solute will form

• we can collect the solvent by condensing it as it evaporates

What’s chromotography?

• seperates solutions with a number of different solutes in the solvent

• place a drop of the solution to be seperated near the bottom of a piece of chromotography paper

• dip the very bottom of the paper into a suitable solvent

• the solvent moves up the paper and carries the solutes in the solution with it

• different solutions move at different speeds so they seperate on the paper

Waht is a special technique of seperating mixtures?

Distillation

What’s simple distillation?

• it seperates 2 liquids with different boiling points

• mixture is heated until the liquid with the lower boiling point starts to boil

• the vapour released passes through a condenser where the gas cools back into a liquid

What’s the timeline of the model of the Atom?

1. Thomson’s plum pudding model- a ball of positive charge with negatively charged electrons

2. Rutherford’s nuclear moddel- discovered that alpha particles could bounce back off atoms so an atom’s mass was concentrated in the atom’s centre called the nucleus

3. Neils Bohr discovered that elctrons orbit the nucleus at fixed distances

4. James Chadwick discovered that some particels in the nucleus have no charge at all called neutrons

What are the 3 different sub-atomic particles?

• Protons

• Electrons

• Neutrons

What are the properties of protons?

• relative charge of +1

• found in nucleus

• an element’s atomic number is the number of protons it has

What are the properties of electrons?

• relative charge of -1

• found in shells around the nucleus

• same number of negative electrons as the protons

What are the properties of neutrons?

• relative charge of 0 as they are neutral

• found in nucleus

How is the periodic table organised?

• periods (the rows) are because of elements with similar properties occur at regular intervals

• group number equals the number of electrons in the outer shell of an atom

What are the properties of metals?

• High melting and boiling points

• Good conductors of heat and electricity

• Solid (except mercury)

What are the properties of non-metals?

• Lower melting and boiling points

• Often found as gases

• Generally do not conduct heat or electricity

What are the properties of Noble Gases?

• Inert (unreactive) as they have a full outer shell and they don’t gain or lose any electrons

• Monatomic- they exist as single atoms instead of forming molecules

• Low boiling point

• Low density

Which group are Noble Gases in?

Group 0

What are the properties of Halogens?

• 7 electrons in outershell

• diatomic molecules- molecules made of pairs of atoms

• Salts are formed when a metal atom transfers it’s outer electron to a non metal atom

• As you go down the group, halogens become less reactive

Which group are Halogens in?

Group 7

Why does the reactivity decrease as you go down group 7?

• atoms gain more electron shells

• making the outer electron shell further from nucleus

• attraction between nucleus and electron decreases

What do the Alkali metals include?

• Lithium- least reactive

• Sodium

• Potassium- more reactive

What makes potassium more reactive than lithium and sodium?

• it is more reactive than lithium and sodium

• as it is least strongly attracted to nucleus

What are the properties of Alkali metals?

• React with water- create metal hydroxide

• React with chlorine- create metal chloride

• React with oxygen- creat metal oxide

What happens with Lithium reacts?

• it burns with a red flame

• effervescence

What happens when Sodium reacts?

• it floats and burns with a yellow/ orange flame

What happens when Potassium reacts?

• it floats and burns with a lilac flame