Chemistry all Y9 Notes & Flashcards [end of years revision]

Separation & Purification, Atomic structure, Ionic bonding, Groups of the periodic table (groups 1, 7, 0)

Physical changes

changes in state that can be reversed and the chemical properties of what you’re changing stay the same

Particle model of gas

random, far apart, moving fast in all directions

Particle model of liquid

random, close, flowing around each other

Particle model of solids

regular, close, vibrating about a fixed position

Filters

things that separate mixtures by letting smaller things through but trapping bigger things (insoluble substances)

Solute

a dissolved substance

Solution

a mix of solutes

Solvent

what solutes dissolve in

Saturated solution

solution containing the most amount of solute that can dissolve in that amount of solvent

Crystallisation definition

a method of separation involving evaporating the solvent to leave the solutes that forms solid crystals

What happens if crystals form slowly in crystallisation

particles have longer to form an ordered pattern and will make larger crystals

What happens if crystals form quickly in crystallisation

particles have less time to form an ordered pattern and will make smaller crystals

Crystallisation risk asessment

• Wear eye protection

• Use steam to heat the evaporating basin gently

• Remove the bunsen burner before the solution is completely dry

• Care must be taken not to overheat the solution as hot crystals may spit out

Crystallisation method

1. The filtrate is placed above a bunsen burner

2. The bunsen burner evaporates the filtrate carefully

3. Crystals are left to cool

4. Crystals are scraped out

5. Crystals are patted dry with cloth / filter paper

What happens if you heat crystals more after they have formed in crystallisation

they may change chemically

Filtration method

1. A filter tunnel is lined with filter paper

2. The solvent and the solute pass through

3. This forms the filtrate

4. Bits of insoluble substances that can’t fit through form the residue

Residue

bits of insoluble substances that don’t get through the filter paper and are left in it

Distillation definition

a way of separating multiple liquids by boiling them one by one

Simple distillation method

1. Liquid is evaporated and turns to gas (vapour)

2. Other materials with higher boiling points are left behind

3. The vapour of the first liquid is now pure. It is condensed back into a liquid

Still

the apparatus used for distillation

Ways to make a still more efficient

• Plugging gaps in apparatus with bungs to stop any gas escaping

• Condenser: a tube surrounded with a jacket of cold water (used instead of a delivery tube). Helps liquid condense quicker with lowered temperatures

• Anti-bumping granules: makes the liquid boil more smoothly, reduces risk of liquid boiling over (put in the solution)

Fractional distillation method

1. Solution is put in a distillation flask and heated

2. The first substance’s vapour (the one with the lowest boiling point) rises up a fractioning column

3. A temperature gradient is created, with the hottest temperatures at the bottom

4. The substance with the lowest boiling point reaches the top first and passes into the condenser and is collected

5. The same happens with the rest of the substances, one by one

Real life examples of fractional distillation

Separate different products of crude oil

Make alcoholic drinks like whisky and vodka

Separate gasses in the air

Composition of a pure substance…

can’t be changed, is the same everywhere in the substance

Can compounds be pure?

yes, if its the only thing in the substance

Mixture

substance containing elements and/or compounds not chemically joined together. they can be separated and don’t have a fixed melting point

Melting point

the temperature at which a substance’s particles gain enough energy to overcome the forces of attraction between them and change state

Mixtures have melting points that…

aren’t fixed, instead they melt over a range of temps. this is because there different things with different melting points inside it

Chromatography

when a solvent moves along paper, different substances in it move at different speeds so separate

Mobile phase in chromatography

the solvent (e.g. water)

Stationary phase in chromatography

the paper

Chromatogram

the piece of paper with the separated components on it

Rf value

distance moved by spot
distance moved by solvent

measurements are made from the starting points of the solvent

Mendeleev

Russian chemist credited with the first periodic table

Mendeleev’s periodic table arrangement

he arranged the elements in increasing order of atomic masses, and elements with similar properties were near each other

Mendeleev’s period table gaps & predictions

He left gaps in his table for unknown elements, and so was able to predict the properties of them by looking at where they fitted and the properties of the elements around them

Mendeleev’s period table faults

His law couldn’t explain the existence of isotopes or where they would go on his table. As they have different atomic masses, they should have been in a separate place, but Mendeleev didn’t give them their column, which didn’t make sense with his law.

Structure of atoms

central nucleus containing protons and neutrons, and electrons arranged in shells surrounding it

What charge do protons have

positive (+1)

What charge do neutrons have

neutral (0)

What charge do electrons have

negative (-1)

Atomic number

number of protons and number of electrons (same for both)

Mass number

number of protons + number of neutrons
aka atomic number + neutrons

How to work out number of protons

atomic number

How to work out number of electrons

atomic number

How to work out number of neutrons

mass number - atomic number

How to tell which one is the mass number

it is always the biggest one

Which number determines what element an atom is

atomic number

Isotope

an atom with the same atomic number but a different mass number. they are the same element but are chemically slightly different as they have a different number of neutrons

How to write isotopes

‘element-mass number’ e.g. chorine-37

mass number in small above, atomic number in small below →

Relative atomic mass definition

weighted average of all an atom’s isotopes

Relative atomic mass equation

(% x mass number of isotope 1) + (% x mass number of isotope 2)
100

How many electrons can the first shell hold

2

How many electrons can the second shell hold

8

How many electrons can the third shell hold

8

How many electrons can the fourth shell hold

8

Writing electron configuration

number of electrons in each shell starting from the middle and going out e.g. 2, 8, 6

Atoms in the same group have…

the same number of electrons in the outer shell

Atoms in the same period have…

the same number of shells

How many electrons in their outer shell do metals have

1, 2 or 3

How many electrons in their outer shell do non-metals have

4, 5, 6 or 7

Staircase line

down from B, metals to the left & non-metals to the right

Transition metals

the middle section of un-grouped metals, the most common metals

Groups

vertical columns in the periodic table, numbered 1-7 with 0 on the end

Periods

horizontal rows in the periodic table, numbered 1-7

Bonds

the forces of attraction that hold atoms together

What happens when bonds are formed between atoms

energy is released, making the atoms more stable & less reactive

Which atoms are the most stable

the ones with a full outer shell as they contain as many electrons as possible (noble gasses)

How do atoms achieve a full outer shell

by transferring their electrons between each other

Ions

charged particles formed by transfer of electrons between atoms

What happens when metals form ions

they loose electrons and form positive ions (cations) which have more protons than electrons

What happens when non-metals form ions

they gain electrons and form negative ions (anions) which have more electrons than protons

What happens to non-metals’ names when they form ions

the end changes to -ide

Electrostatic forces

the forces of attraction between all positively and negatively charged objects, they hold oppositely charged ions together and form an ionic bond between them

Which atoms will easily form ions

ones that have a nearly full / nearly empty outer shell

What happens when group 1 elements form ions

they have 1 outer electron, so loose one to be come a positively charged ion, 1+

What happens when group 2 elements form ions

they have 2 outer electrons, so loose two to become a positively charged ion, 2+

What happens when group 6 elements form ions

they have 6 outer electrons so gain two to become a negatively charged ion, 2-

What happens when group 7 elements form ions

they have 7 outer electrons so gain one to become a negatively charged ion, 1-

Why is group one called alkali metals

they react with water to form alkalis

What are some physical properties of group 1

low melting points, soft and easily cut, very reactive, readily form compounds with non-metals

What happens when lithium reacts with water

it bubbles fiercely on the surface

makes lithium hydroxide and hydrogen gas

What happens when sodium reacts with water

it melts into a ball and fizzes about the surface

makes sodium hydroxide and hydrogen gas

What happens when potassium reacts with water

it bursts into lilac flame and flies about the surface

makes potassium hydroxide and hydrogen gas

Reactivity trend for group 1

as you go down the group, reactivity increases

Similarities in group 7

exist as diatomic molecules, are non-metals, are poor conductors of heat & electricity, all toxic & corrosive

Trend in melting/boiling point in group 7

as you go down the group, melting/boiling point increases

Trend in density in group 7

as you go down the group, density increases

What do group 7 elements form when they react with metals

salts

Why can group 7 elements be used as disinfectants/bleaches

they can kill microorganisms and remove colour from materials

Test for chlorine

put damp blue litmus paper in chlorine it will turn red and then bleach

What do group 7 elements form when reacting with hydrogen

hydrogen halides

What is produced when hydrogen halides dissolve in water

they form acids e.g. hydrochloric acid

Reactivity trend in group 7

reactivity decreases as you go down the group

Displacement reaction

reaction where a more reactive element takes the place of a less reactive element in a compound

Similarities in group 0

colourless, have low melting/boiling points, are poor conductors of heat/electricity, inert

Inert

doesn’t easily react with anything

Why are noble gasses inert

they have a full outer shell already

Melting/boiling points trend in group 0

decreases as you go down the group (but are all very low)

Uses of krypton

photography lighting because it produces a bright white light when electricity is passed through it