C1: Atomic structure and the periodic table Flashcards
define an atom
the smallest part of an element that can exist
define an ‘element’
a substance of only one type of atom
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define a compound
two or more elements combined chemically in fixed proportions which can be represented by formulae
what is a mixture? Does it have the same chemical properties as its constituent materials?
- a mixture consists of two or more elements or compounds not chemically combined together
- it does have the same chemical properties
give the 5 methods mixtures can be separated? do they involve chemical reactions?
- filtration, crystallisation, simple distillation, fractional distillation , chromatography
- they do not involve chemical reactions
describe and explain simple distillation.
- used to separate liquid from a solid
- the liquid is heated
- the vapour then rises and cools in the condenser and drips into a beaker
- solid is left in the flask and liquid is left in the beaker
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Describe and explain crystallisation
- Crystallisation is used to produce solid crystals from a solution.
- a solution is placed in an evaporating basin and heated with a Bunsen burner
- the volume of the solution decreases as some of the water has evaporated
- solid particles begin to form in the basin
- the water then evaporates leaving crystals behind
describe and explain fractional distillation
describe and explain fractional distillation
- The solution is heated to the temperature of the substance with the lowest boiling point
- This substance will rise and evaporate first, and vapours will pass through a condenser, where they cool and condense, turning into a liquid that will be collected in a beaker
- All of the substance is evaporated and collected, leaving behind the other components(s) of the mixture
- the same thing occurs with the temperature of the next substance
Describe and explain filtration
- used to separate an insoluble solid suspended in a liquid
- one beaker contains a mixture of solid + liquid the other a funnel with filter paper
- this is poured into the filter funnel
- the insoluble solid gets caught in the filter paper as particles are too large
- the filtrate is the substance that comes through the filter paper
what is chromatography used for?
- used to separate a mixture of substances dissolved in a solvent.
describe and explain paper chromatography
- A pencil line is drawn on chromatography paper and spots of the sample are placed on it.
- The paper is then lowered into the solvent container, making sure that the pencil line sits above the level of the solvent, so the samples don’t wash into the solvent container
- The solvent travels up the paper by capillary action, taking some of the coloured substances with it
- Those substances with higher solubility will travel further than the others
- This will show the different components of the ink / dye
The plum pudding model of the atom was replaced by the nuclear model.
The nuclear model was developed after the alpha particle scattering
experiment.
Compare the plum pudding model with the nuclear model of the atom
similarities :
- both have positive charges
* both have (negative) electron
differences:
- in ppm mass is spread throughout whereas in the nm mass is concentrated at the centre
- in the ppm electrons are spread throughout whereas in the NM electrons are outside the nucleus
describe the plum-pudding model and who proposed it
- the atom is a ball of positive charge with negative electrons embedded in it
- JJ Thompson
Evidence from the alpha particle scattering experiment
led to a change in the model of the atom from the plum pudding model.
Explain how.
- most (alpha) particles passed (straight) through (the gold foil)
- (so) the mass of the atom is concentrated in the nucleus
so most of the atom is empty space - some (alpha) particles were deflected / reflected
- (so) the atom has a (positively) charged nucleus
describe the Bohr/ nuclear model and how it came about
- the nuclear model suggests that electrons orbit the nucleus at specific distances (shells)
- it came about from alpha scattering experiments
what did the work of James Chadwick provide evidence for?
- the existence of neutrons in the nucleus
Chadwick’s experimental work on the atom led to a better understanding of
isotopes.
Explain how his work led to this understanding
- Chadwick provided the evidence to show the existence of neutrons
- (this was necessary because) isotopes are atoms of the same
element - but with different numbers of neutrons
describe the structure of an atom
- the atom has a small central nucleus which is made up of protons and neutrons around which there are electrons
State the masses of the
subatomic particles
Protons: 1, neutrons: 1, electrons: 0
State the relative charges
of the subatomic particles
Protons: +1, neutrons: 0, electrons: -1
what is the radius of an atom
0.1 nm or 1 x 10 ^ -10
what is the radius of a nucleus and what is it compared to that of the atom
1 x 10 ^ -14
what name is given to the number of protons in the nucleus
atomic number
atoms of the same element have the same number of which particle in the nucleus
protons
where is the majority of mass of an atom
the nucleus
define the mass number
the total number of protons and neutrons
define an isotope
- atoms of the same element that have a different number of neutrons but same number or protons
what is the relative atomic mass?
- the average mass value which takes the mass and abundance of isotopes of an element into account
define an ion
- ions are charged particles.
- they are formed when atoms lose electrons ( positive ions) or gain ( negative ions) electrons
give 6 properties of metals
metals:
- high boiling point
- conducts heat and electricity
- shiny
- it is malleable
- high density
- basic oxides
give the 6 properties of non-metals
non-metals:
- low boiling point
- does not conduct heat or electricity
- dull appearance
- brittle malleability
- low density
- acidic oxides
what is formed when a metal reacts with a non-metal
- an ionic compound
what is formed when a non-metal reacts with a non-metal
- a molecular compound containing covalently bonded atoms
- atoms share electrons as opposed to transferring electrons between each other
define these terms:
- solute, solvent, solution
- miscible
- a solute is a substance that is dissolved in a solvent, these form a solution
- miscible refers to the substances that mix together
- soluble: the substance that can be dissolved in a solvent
are elements in the same group similar or different
- they may have similar chemical properties, as they have the same number of outer shell electrons
what are the elements of group 0 known as?
- the noble gases
What can the period tell
you about the electrons in
an atom?
How many shells an atom has.
Why did Mendeleev put
some elements in groups?
Because they had similar chemical properties (e.g. they
reacted violently with water)
Why did Mendeleev leave
gaps in his periodic table?
For elements that had not been discovered yet
What can the group tell
you about the electrons in
an atom?
How many electrons in the outer shell. E.g. carbon is in
group 4 so has 4 electrons in the outer shell
Why did Mendeleev put
some elements in groups?
Because they had similar chemical properties (e.g. they
reacted violently with water)
why were early periodic tables incomplete and placed in the incorrect groups
as they were placed in the strict order of atomic weights
what made it possible to explain why the order based on atomic weights was not always correct
- knowledge of isotopes
elements that react to form positive ions are…
metals
state three characteristics of the alkali metals
- all have one electron in their outer shell
- are stored under oil ( to prevent reactions with oxygen or water
- are soft ( can be cut with knife)
how do group zero elements react with non-metals
- they form compounds which are soluble white solids which form colourless solutions
how do group1 elements react with water?
- they release hydrogen and form hydroxides which dissolve to form alkaline solutions
- react vigorously with water by fizzing and moving around on water surface with high energy
how does reactivity differ moving down group 1 and why?
- reactivity increases
- the atoms get larger and the distance between the nucleus and the outer electrons increases
- thus electrostatic attraction from the nucleus decreases
- allowing them to more easily lose electrons
state 5 characteristics of group 7
- 7 electrons in the outer shell
- coloured vapours
- diatomic molecules
- form ionic salts with metals
- form molecular compounds with non-metals
state 4 group 7 elements ; their state of matter ; and colour formed
fluorine, is a pale yellow gas
chlorine, is a pale green gas
bromine, dark brown liquid
iodine, is a grey solid
state three changes that occur in group 7 as one moves down the group
- higher relative molecular mass
- higher melting and boiling point
- reactivity decreases - less easily gain electrons
What is a displacement
reaction?
A reaction in which a more reactive element takes the
place of a less reactive element in a compound
. Balance the below
equation and explain why it
is a displacement reaction:
KBr + Cl₂ → KCl + Br₂
2KBr + Cl₂ → 2KCl + Br₂ , chlorine has displaced bromine as
it is more reactive
Explain why bromine is less
reactive than chlorine (3
marks)
- More shells/electrons,
- more shielding (or weaker attraction
from nucleus) - harder to gain electrons
Explain why sodium is less
reactive than caesium (3
marks)
- Fewer shells/electrons
- less shielding due to a stronger electrostatic attraction from nucleus
- thus it is harder to lose electrons
give 6 properties of transition metals in comparison to group 1 metals
- harder and stronger metals
- higher melting points ( other than mercury)
- high density
- less reactive then group 1 metals
- can form ions with different charges
- react with oxygen to form metal oxides
define inert and explain why the noble gases are inert
- unreactive
- they have full outer shells, so do not need to gain or lose electrons
state three common characteristics of transition metals
- ions with different charges
- coloured compounds
- catalytic properties
define the term ‘ catalyst’
- a chemical substance that increases the rate of a chemical reaction
- it is not used up over the course of the reaction
state the colours of flames observed when lithium sodium and potassium burn in oxygen
li - crimson red
Na- yellow-orange
K- lilac
describe the properties of noble gases. discuss the trends in properties down the group
- non-metals, gases, low boiling points
- the boiling point increases down the group, as the atoms get heavier
