Elements, Mixtures and Compounds

An atom has 13 protons and 14 neutrons. What is its mass number?

27

What are isotopes?

atoms of the same element (with the same number of protons) but with a different number of neutrons

What is a compound?

a substance made up of 2 or more elements that are chemically combined (in fixed proportions)

What does endothermic mean?

absorbs heat from the surroundings

What does exothermic mean?

releases heat into surroundings

What happens to solids when they are heated?

they expand (the hotter a solid gets, the faster its particles vibrate. This means that solids expand when they're heated)

What is a molecule?

2 or more atoms bonded together

What is an element?

a substance that contains only ONE type of atom

Where are protons found?

nucleus of an atom

Where are neutrons found?

nucleus of an atom

Where are electrons found?

in shells surrounding the nucleus

What does the atomic number tell you?

the number of protons in the nucleus of an atom

What does the mass number tell you?

total number of protons and neutrons / total number of subatomic particles in the nucleus of an atom

How do you work out the number of neutrons?

mass number - atomic number

How are substances separated in paper chromatography?

The substance's attraction to the mobile phase only, each substance has a different attraction to each phase so travels up the paper by a different amount, allowing the mixture to be separated.

What property of the sand allows it to be removed from the water by filtration?

sand is an insoluble solid

What is an atom made up of?

subatomic particles; neutrons, protons and electrons

What is the relative mass of a proton?

1

What is the relative mass of a neutron?

1

What is the relative mass of a electron?

1/2000

What is the relative charge of a electron?

-1 (negative electric charge)

What is the relative charge of a proton?

+1 (positive electric charge)

What is the relative charge of a neutron?

0 (no electric charge)

How much electric charge does an atom have?

atoms are neutral, meaning they have a total of zero electric charge

What does the number of protons and electrons in an atom have in common?

atoms contain the same amount of protons and electrons (to maintain the atom/zero charge)

What do you call an atom that has lost electrons?

a positive ion

What do you call an atom that has gained electrons?

a negative ion

How are elements in the periodic table organised?

in order of increasing atomic number (from left to right) and their properties

What do elements in a group have in common (atom-wise)?

they have the same number of electrons in the outer/last shell

What do elements in a period have in common (atom-wise)?

they have the same number of shells around their atom

Is a group a horizontal or vertical line on the periodic table?

vertical

Is a period a horizontal or vertical line on the periodic table?

horizontal

What are the four separation techniques?

filtration, evaporation, distillation, crystalisation

What is a pure substance?

a substance made up of only one type of element or one type of compound

Can you use separation techniques with a pure substance?

no, a pure substance can't be separated into anything simpler without a chemical reaction

What is a mixture?

a combination of two or more substances that are not chemically combined (e.g. sea water and air)

Can you use separation techniques with a mixture?

yes, a mixture can be separated using physical methods because the substances aren't chemically joined

What is a solute?

the substance being dissolved

What is a solvent?

the substance in which the solute dissolves

What is a solution?

a mixture of a solute and a solvent (that does not separate out)

What does soluble mean?

it will dissolve

What does insoluble mean?

it won't dissolve

What is solubility?

the measure of how much solute will dissolve in a solvent

What does filtration do?

separates insoluble solids from liquids (mixtures)

What equipment is needed for filtration? (3)

• funnel

• filter paper

• beaker

What does evaporation do?

separates a soluble solid from a liquid

What equipment is needed for evaporation? (3)

• bunsen burner

• evaporating dish/crucible

• tripod

What are the steps of evaporation? (2 steps)

1. Place solution in an evaporating dish/crucible and place it on a tripod.

2. Slowly heat it with a bunsen burner.

Why do crystals form during evaporation?

Because as the solvent (liquid) begins to evaporate, the remaining solution will become more concentrated. When the solution becomes so concentrated, crystals will begin to form.

What is thermal decomposition?

the breaking down of a substance by heating

What does crystallisation do?

separates a soluble solid, which is vulnerable to thermal decomposition, from a solution.

What equipment is needed for crystallisation? (6)

• evaporating dish/crucible

• water bath (or any gentle heating mechanism)

• tripod

• funnel

• filter paper

• source of heat (e.g. over or sun)

What are the steps of crystallisation? (5 steps)

1. Place solution into an evaporating dish/ crucible.

2. Very gently heat the solution (e.g. using a water bath).

3. Once some of the solvent has evaporated and you can start to see crystals forming, stop heating and leave it to cool.

4. Filter out the crystals from the remaining solution, using filtration.

5. Dry crystals, using heat (e.g. oven or somewhere warm)

What does (simple) distillation do?

separates a solute and solvent or a solvent from solvent, but keeps the solvents.

What equipment do you need for simple distillation? (7)

• flask

• bunsen burner

• bung

• thermometer

• condenser

• water jacket

• beaker

What happens during distillation?

A liquid is boiled to produce steam which rises to the top of the flask, forcing it down the condenser where the liquid condenses back to a liquid (because of the continuously flowing cold water in the water jacket). The liquid will then run down the pipe into a beaker.

What is the conservation of mass?

atoms cannot be made or destroyed

What is chromatography?

a separation technique and/or a method to identify substances in a mixture

Who made the first accepted periodic table and when?

Dmitri Mendeleev, in 1869

What two things did Dmitri Mendeleev do differently with his periodic table?

• left gaps for elements he predicted had yet to be discovered

• was prepared to alter slightly the order of the elements

What are miscible liquids?

liquids that mix

What are immiscible liquids?

liquids that do not mix completely, but separate into layers due to differences in densities

What is an example of when you would use filtration?

to separate sand from water

What is an example of when you would use evaporation?

to separate salt from water

What is an example of when you would use crystallisation?

to separate copper sulphate crystals from a solution of copper sulphate

What is an example of when you would use simple distillation?

to separate pure water from sea water

What is the Rf calculation? (chromatography)

Rf = distance travelled by substance / distance travelled by solvent

If red ink travelled 3cm up filter paper, and the water travelled 4cm up the filter paper. What is the Rf value?

0.75cm

What are the alkali metals?

Group 1 : Lithium, Sodium, Potassium, Rubidium, Cesium, Francium

What are 3 properties of the alkali metals?

• soft, it is easy to cut them

• appear to be dull, because they react with the oxygen in the air

• react with water to make an alkali

How many electrons are in the outer shell of the alkali metals (group 1)?

one electron in their outer shell

How many electrons are in the outer shell of the noble gases (group 0)?

eight electrons in their outer shell (full outer shell)

Why is group 1 so reactive, but group 0 is unreactive?

Because the atoms in group 1 want to get rid of the electron on their outer shell desperately to become stable. This means they react with more atoms/elements in order to get rid of the electron on their outer shell. Whereas group 0's atoms are stable and do not want to lose any electrons.

What is an atom's main goal?

to have a full outer shell

When you go down group 1 (Alkali metals) does the reactivity increase, decrease or stay the same?

increase

When you go down group 7 (Halogens) does the reactivity increase, decrease or stay the same?

decrease

When you go down group 0 (Noble gases) does the reactivity increase, decrease or stay the same?

stay the same

When you go down group 7 (Halogens) do the melting and boiling points increase, decrease or stay the same?

increase

When you go down group 1 (Alkali metals) do the melting and boiling points increase, decrease or stay the same?

decrease

When you go down group 0 (Noble gases) do the melting and boiling points increase, decrease or stay the same?

increase

A gas is tested with a burning splint and produces a squeaky pop. What gas is it?

hydrogen

How can you tell from a chromatogram how many substances were present in the mixture?

from the number of spots made from the original mixture is the number of different substances in the mixture

Which gas causes damp blue litmus paper to turn white?

chlorine

What are the elements in between the groups called on the periodic table? (e.g. Au - gold)

Transition Metals

What does (aq) mean?

aqueous (dissolved in water)

What is an atom?

building block of the universe

As you go down a group are the outer electrons nearer or further from the nucleus?

further

As you go down a group is the attraction between the nucleus and the outer electrons getting stronger or weaker?

weaker

Describe what happens when an alkali metal is put into water?

they produce heat (flame), hydrogen gas (the fizz and gas created), the corresponding metal hydroxide and they turn the water into an alkali solution

How did Mendleev organize his periodic table?

by increasing atomic mass and properties

What is the stationary phase in chromatography?

phase in chromatography that does not move/non-moving phase (the fixed point where you make measurements from/pencil line)

What is the mobile phase in chromatography?

phase in chromatography that moves (the solvent that moves through the paper, carrying different substances with it_

What is a formulation?

a mixture that has been designed to do something useful, that has required properties

If a substance is impure the melting point will be __________ and the substance will melt over a broad range of temperatures.

lower

If a substance is impure the boiling point will be __________ than the pure substance.

higher

Write a method for separating and identifying the dyes in a food colouring. (5 steps)

1. Draw a pencil line across the chromatography paper, 1-2cm from the bottom

2. Use a pipette to add small spots of each dye to the line on the paper

3. Place the paper into a beaker with water at the bottom

4. Let the solvent move up the paper, but remove the paper before the water reaches the top

5. Let the paper dry, then identify which dyes match with the mixture

Write the method for making copper sulphate crystals. (7 steps)

1. Place some sulfuric acid in a flask and warm it in a water bath

2. Add a spatula of copper oxide powder to the acid and stir with a glass rod

3. Continue adding copper oxide powder until it is in excess

4. Filter the mixture to remove the excess copper oxide

5. Pour the filtrate (the copper sulphate solution) into an evaporating basin

6. Heat the copper sulphate solution to evaporate half of the water

7. Pour the solution into a watch glass and leave to allow all of the water to evaporate

What is sublimation?

the change of state from a solid to gas (without becoming a liquid in between)