Elements, Compounds And Mixtures Flashcards
Element
A pure substance made of only one type of atom.
Compound
A substance made of two or more different types of atoms chemically bonded together.
Mixture
Two or more different types of atoms mixed together, NOT chemically bonded
Mg 2+ + Br- =
MgBr2
Mr
Relative formula mass
Ar
Relative atomic mass
Percentage composition
Ar of an element
————————. X 100
Mr of a compound
What processes can be used to separate mixtures (4)
- distillation
- chromatography
- filtration
- evaporation
Rf value
Distance travelled by substance
————- ———————- - ——-
Total distance travelled by solvent
What does chromatography separate and how
Separates soluble liquids. They have different solubilities so they travel different distances up the paper.
Molecule
Group of atoms chemically bonded together
Signs of a chemical reaction (5)
- colour change
- effervescence, fizzing or bubbling
- change in mass
- change in temperature
- formation of a precipitate
How does the total relative mass of reactants compare to the products
They are equal
Percentage yield formula
Actual mass
— ——————- X 100
Theoretical mass
Steps for finding reacting mass
- Find the Mr of the element/compound reactant and product
- Add units (g) to this number
- Make the reactant mass into 1g by dividing both numbers by the reactant mass
- Multiply the numbers by the mass of the reactant in the question
Avagrado’s constant
6.02 x 10 to the power of 23
Mole
An amount of substance that contains the same number of atoms present in 12 g of carbon 12
Number of moles =
Mass
— ——
Molar mass
Units for mole
g/mol
charge of a proton
+1
charge of a neutron
0
charge of an electron
-1
charge of an atom
neutral
mass number
number of protons and neutrons in the nucleus
atomic number
number of protons in the nucleus (and electrons in electron shells)
characteristics of group 1 metals (6)
- conductors
- soft
- low - melting point
- low density
- stored in oil
- shiny when freshly cut
characteristics of group 7 halogens (5)
- toxic
- non conductive
- low melting/boiling point
- brittle if solid
- become darker in colour as you descend the group
what do alkali metals react with water to form
react vigorously with water to form metal hydroxide + hydrogen
what do alkali metals react with air to form
metal oxide
what do halogens react with metal to form
metal halides
how is reactivity affected as you move down group 1
it increases
how is reactivity affected as you move down group 7
it decreases
how are melting/boiling points affected as you descend group 1
they decrease
how are melting/boiling points affected as you descend group 7
they increase ( at room temp chlorine is a gas, bromine is a liquid and iodine is a solid)
Which are more reactive group 1 or 2 elements and why
Group 1 as losing 1 electron is easier than losing 2
Which are more reactive group 6 or 7 elements and why
Group 7 elements as gaining 1 more electron is easier than gaining 2
Explain the reactivity of elements as you descend group 1
As you descend group 1, reactivity increases. All of the elements have 1 electron in their outer shell and therefore need to lose one electron to have a full outer shell. As you move down the group distance between the nucleus and outer shell increases, decreasing force of attraction. This makes it easier to lose an electron. Lithium finds it difficult to lose an electron while potassium finds it easier.
Explain the reactivity of elements as you descend group 7
As you descend group 7, reactivity decreases. All of the elements have 7 electrons in their outer shell and therefore need to gain an electron to have a full outer shell. As you descend the group distance between the nucleus and outer shell increases, decreasing the force of attraction. Therefore, it becomes more difficult to gain an electron as you descend the group. Fluorine gains electrons easily while bromine finds it more difficult to gain electrons.
Observations of reactions of alkali metals with oxygen
Tarnishing of freshly cut surface. They tarnish quicker if they are more reactive.
What pH are metal hydroxides
Alkaline
What colour does lithium burn in combustion reaction with oxygen
Burns with crimson/red flame
What colour does sodium burn in a combustion reaction with oxygen
Yellow/orange flame
What colour does potassium burn in a combustion reaction with oxygen
Lilac flame
Word equation for reaction of alkali metal with oxygen
Alkaline metal + oxygen —-> metal oxide
Symbol equation for reaction of lithium with oxygen
4Li + 02 —> 2Li2O
Observations of lithium reaction with water
moves slowly around the surface of the water, fizzes (effervescence)
Observations of sodium reaction with water
fizzes and forms a molten ball that moves quicker on the waters surface
Observations of potassium reaction with water
lilac flame and moves very quickly on the waters surface, forms a molten ball
Symbol equation for reaction of lithium with water
2Li + 2H2O —-> 2LiOH + H2
Word equation for reaction of alkali metal and halogen
Alkali metal + halogen —-> Alkali metal halide
Word equation for potassium reaction with chlorine
Potassium + chlorine —> potassium chloride
Symbol equation for reaction of lithium with bromine
2Li + Br2 —> 2LiBr
What do all alkali metal halides look like
White solids
Test used to identify hydrogen gas
Gather gas into test tube. Hold a little splint in the test tube. If hydrogen gas is present a squeaky pop is observed
Colour of bromine at room temp
Brown/red
Colour of iodine at room temp
Blue/black
Colour of chlorine at room temp
Pale, yellow/green
Word equation for reaction of halogen with iron
Iron + halogen —-> iron(III) halide (salt)
Iron + chlorine
2Fe + 3Cl2 —> 2FeCl3
Why are displacement reactions of halogens better evidence than reactions with iron for reactivity
The halogens different states at room temp make it difficult to compare reactivities based on observation
What colour are halide solutions
Colourless
What colour does the solution turn if chlorine displaces bromine
Orange/brown
Word equation for sodium bromide + chlorine
Sodium bromide + chlorine —> sodium chloride + bromine (s)
What colour does does the solution turn when bromine displaces iodine
Red-brown
Symbol equation for sodium iodide + bromine
2NaI + Br2 —> 2NaBr + I2
Properties of chlorine/iodine
Toxic/poisonous, kill bacteria
A Use of chlorine
Treatment of water supplies
Use of iodine
Used as antiseptic following hospital procedures
What colour is a calcium flame
Brick red
What colour is barium flame
Apple green
What colour does sodium chloride turn with silver nitrate
White
What colour does sodium bromide turn with silver nitrate
Cream
What colour does sodium iodide turn with silver nitrate
Yellow
Word equation for sodium chloride + silver nitrate
Sodium chloride + silver nitrate —> sodium nitrate + silver chloride
Symbol equations for silver nitrate + sodium bromide
AgNO3(aq) + NaBr(aq) —> NaNO3(aq) + AgBr(s)
Ionic equation for silver nitrate + sodium iodide
Ag+(aq) + I-(aq) —> AgI(s)
Properties of helium
Very low density, unreactive
Properties of neon
Emits light when electric current is passed through it
Argon
Unreactive
Use of helium
Used in airships
Use of neon
Used in advertising signs
Use of argon
An an inert atmosphere for welding or in light bulbs
what can be observed in the reaction between iron wool and chlorine gas
it glows brightly
