Chapter 1 - Atomic Structure and the Periodic Table Flashcards
define elements
all of the atoms in an element are the same
define compounds
2 or more different elements chemically combined in fixed proportion
how are compounds seperated
they can only be seperated by a chemical reaction
do compounds have the same properties to the elements they are made of?
no, usually they have different properties
define mixtures
different elements or compounds not chemically combined
how are mixtures seperated
by physical seperation techniques
give examples of physical seperation techniques
filtration
distillation
crystallisation
chromatography
define molecule
any elements that are chemically combined (it can also be the same elements)
give 2 examples of a molecule
NH3 (ammonia) - compound + molecule
O2 (oxygen) - element + molecule
what are all the diatomic molecules
O2 (oxygen)
H2 (hydrogen)
N2 (nitrogen)
F2 (fluorine)
Cl2 (chlorine)
Br2 (bromine)
I2 (iodine)
define chemical formula
chemical formula tells us the elements in a molecule and the number of atoms of each element
how can you tell the number of atoms of each element using a chemical formula
by looking at the small number next to the symbol of the element
what happens when you change one of the small numbers next to an element’s symbol in a compound?
you get a completely different compound.
the atoms in a compound MUST be in fixed proportion
what does filtration do
seperated insoluble solid from a liquid
define insoluble
does not dissolve in liquid
what do state symbols say
they tell us the physical state of a chemical
tell me the state symbols of solids, liquids, gases, and solutions
solid – (s)
liquid – (l)
gas – (g)
solution/dissolved in water – (aq)
what happens during filtration
- pour mixture into filter paper
- liquid passes through the tiny pores in the filter paper (this liquid is called the filtrate)
- solid doesn’t pass through the filter paper
- liquid is now seperated from the solid
what does crystallisation do?
seperates soluble solid from liquid
(i.e. seperated solution)
what happens during crystallisation
- the solution is gently heated to evaporated the water
- the solution is left to evaporate the rest of liquid
- the liquid is seperated from the solid.
- solid is left over in the form of crystals
why might speeding up crystallisation by heating not be a good idea
certain chemicals will break down if we heat them, so it may not be a good idea if we want to keep the solid
explain how we can tell crystallisation is a physical seperation technique
the formula of the solid does not change, so no new products have been formed
what does simple distillation do
seperates soluble solid from liquid, while keeping the liquid
what happens during simple distillation
- evaporate liquid by heating (usually until it boils), the liquid turns into vapour
- condense the vapour back to liquid by cooling
- Left with crystals (solid) and the liquid
what is simple distillation sometimes used for
to produce drinking water from sea water
why might people not use simple distillation to produce drinking water
simple distillation requires lots of energy, so it is very expensive to do regularly
what does fractional distillation do
seperates mixture of different liquids with different boiling points
what happens during fractional distillation
- The mixture of liquid is heated, until they are evaporating
- The liquid with a lower boiling point (BP) will evaporate more easily
- When the vapours reach the fractionating column, they condense and drip back into the flask where they evaporate again
- Repeated evaporation and condensation increases the amount of the lower boiling point chemical in the fractionating column.
- The warm vapours go up the column and reach the thermometer and the temperature rises (rising temperature means different vapours are passing, the mixture contains more of the chemical with lower BP)
- At one point, the temp of the thermometer becomes constant (the lower BP) - this means that 1 chemical is passing through the condenser.
- These vapours pass through the condenser, turn into liquid and are collected. (the 1st liquid)
- The temp rises again (mixture contains more of the chemical with higher BP)
- The temperature becomes constant again (the higher BP)
- The vapours pass through the condenser, turn into liquid and are collected. (the 2nd liquid)
what happens if there is a mixture of liquids with similar boiling points?
it will be harder to seperate
we would need to do several rounds of fractional distillation
what does paper chromatography do
allows us to seperate substances based on their different solubilities
what happens during paper chromatography
- Take a chromatography paper, draw a pencil line towards the bottom
- Put dot A and dot B on the pencil line (can do more)
- Place bottom of paper into a solvent
- The solvent makes its way up the paper + dissolves the ink of the dots
- Ink in carried up the paper dissolved in the solvent
define solvent
liquid that will dissolve substances
what is the stationary phase
paper
what is the mobile phase
solvent
how can you tell if something is a pure compound using chromatography
they produce a single spot in all solvents
how can you tell if something is a mixture using chromatography
they seperate into different spots depending on the solvent
why does a more soluble substance travel further
it is more attracted to the mobile phase (solvent)
what is everything made of
atoms
what were the initial beliefs about the atom
- atoms are tiny spheres that cannot be divided
- in 1897, negative particles (electrons) were discovered
what is the plum pudding model
atom is a ball of positive charge with negative electrons embedded in it.
describe the alpha scattering experiment
There is a piece of gold foil (because we can hammer it into really thin foil, just a few atoms thick)
Tiny alpha particles were fired at the gold foil
what observations were made in the alpha scattering experiment
- Most of the alpha particles passes straight through
- Sometimes, an alpha particle was deflected
- Sometimes, an alpha particle bounced back off the foil
what conclusions were made because of the alpha scattering experiment
- Atoms are mainly empty space
- The centre of the atom is positively charges (nucleus)
- The centre of the atom contains a great deal of mass
draw the nucleur model
what modifications have been made to the nucleur model
Nield Bohr discovers that electrons orbin the nucleus at specific distances. These are now called ‘energy levels’ or ‘shells’
Scientists found that the positive charge in the nucleus is due to tiny positive particles (protons)
James Chadwick discovered that the nucleus also contains neutral particles (neutrons)
what is the size of the radius of an atom
1x10⁻¹⁰ m
OR
0.1 nm
what is the size of the radius of the nucleus
1x10⁻¹⁴ m
what is the relative charges of protons, neutrons and electrons
Protons: +1
Neutrons: 0
Electrons: -1
what is the relative masses of protons, neutrons and electrons
Protons: 1
Neutrons: 1
Electrons: very small
why do atoms have no overall charge
the number of protons and electrons are the same, so they cancel each other out.
neutrons do not have a charge
define relative mass
the mass of one particle compared to the mass of another particle
define relative charge
the charge of one particle compared to the charge of another particle
draw the final nucleur model
where is the mass number and what does it indicate
it is at the top of the element, it gives us the number of protons and neutrons
where is the atomic number and what does it indicate
it is at the bottom of the element, it gives us the number of protons and electrons (which are the same)
how can you find the number of neutrons
mass no. - atomic no.
Is the number of neutrons always the same
No, the number of protons are always the same, but the number of neutrons is not fixed
define isotopes
atoms of the same element with different numbers of neutrons
define ions
atoms which have an overall charge, because they have gaines/lost electrons
postive ions:
negative ions:
lose electons
gain electrons
define abundance
how common each isotope is
define relative atomic mass
the weighted average of the different isotopes of an atom
formula for relative atomic mass
how many electrons can the 1st energy level in an atom hold
2
how many electrons can the 2nd, 3rd… energy levels hold
8
what does the number of electrons in the outer shell of an atom tell us
the group number of that element in the periodic table
where are the groups in the periodic table
they are the vertical columns
where are elements with full outer energy levels found
in group 0
what do scientists call group 0
the noble gases
why is the periodic table called as such
elements with similar properties occur at regular intervals
what is the similarity between elements of the same group
they all have similar properties
they have the same number of electrons in their outer shell
describe Dobereiner’s Triads
He notices that elements with similar chemical properties ofter occurred in threes.
Scientists began to wonder if there was a pattern to the elements
describe Newland’s Octaves
He arranged elements in order of atomic weight.
He noticed that every 8th element reacts in a similar way
what were some problems with Newland’s idea
by always sticking to the exact order of atomic weight, elements of different properties were sometimes grouped together
what did Dmitri Mendeleev do?
He developed the first modern periodic table
what did Dmitri Mendeleev do differently to other scientists.
Although he started by arranging all the elements in order of increasing atomic weight, he would switch some elements around so that they would fit the patterns of other elements in the same group
He also left gaps for undiscovered elements and predicted their properties
what are the differences between Dmitri Mendeleev’s period table and the modern period table
The modern periodic table is arranged by atomic number. (protons were not discovered during Mendeleev’s time)
The modern periodic table had a Group 0
(these elements had not been discovered yet during Mendeleev’s time)
what type of elements are the noble gases?
very unreactive elements
where in the periodic table can we find the noble gases
Group 0
why are the noble gases unreactive
all of their outer energy levels are full, this makde atoms stable (unreactive)
describe how the boiling points of Group 0 (the noble gases) vary as we go down the group
they all have boiling points lower that room temperature, as they are gases
the boiling point increases as the relative atomic mass increases (increases as it goes down the group)
where are metals found in the periodic table
on the left (groups 1 and 2) and centre (transition metals)
where are non-metals found in the periodic table
on the right
what type of metals are groups 1 and 2
highly reactive metals
what happens when metals react
they lose electrons to get a full outer shell (gives them the stable electronic structure of a Group 0 noble gas)
what happens to a metal atom when it loses electrons
the atoms now have an overall charge
the atom has turned to an ion
metals always form postive ions
what are group 1 metals known as
the alkali metals
are alkali metals soft or hard?
soft
how do alkali metals react with oxygen
they react rapidly, more rapidly as we go down the group
explain how alkali metals react with oxygen in terms of electrons
Example:
2 lithium atoms react with 1 oxygen atom to get a full outer shell.
The lithium atom turns to a +1 lithium ion
The oxygen atom turns to a 2- oxide ion
All Group 1 metals react in this way with oxygen
what is the equation for the reaction between lithium and oxygen
4Li + O₂ –> 2Li₂O
how do alkali metals react with chlorine
they react rapidly
explain how alkali metals react with chlorine in terms of electrons
Example:
1 lithium atom reacts with 1 chlorine atom to get a full outer shell.
The lithium atom turns to a +1 lithium ion
The chlorine atom turns to a 1- chloride ion
All Group 1 metals react in this way with chlorine
what is the equation for the reaction between lithium and chlorine
2Li + Cl₂ –> 2LiCl
equation for alkali metal reacting with water
lithium + water —> lithium hydroxide (alkali) + hydrogen (gas)
2Li + 2H₂O —> LiOH + H₂
describe the reactivity of Group 1 metals
more reactive as it goes down the group
why are metals more reactive as we go down the group
there is a greater distance between the positive nucleus and the outer electron, so there is less attraction.
this makes the electron easier to lose, therefore more reactive
what are group 7 elements called
the halogens
they are non-metals
define covalent bond
sharing of electrons to make a full outer shell
are the halogens molecules?
yes, they are molecules with 2 atoms, joined by a covalent bond
How can you tell if an element is a solid/liquid/gas at room temperature?
solid: mp + bp is higher than room temperature
liquid: mp is lower than room temp, bp is higher than room temp
gas: mp + bp is lower than room temp
define relative molecular mass (RMM)
it gives an idea of the size of a molecule
describe the relationship between relative molecular mass and group 7 elements
as we move down the group, the RMM increases (molecules get bigger)
what do halogens form when reacted with a non-metal
a covalent bond
what do halogens form when reacted with a metal
an ionic compound
they gain 1 electron and always from an ion with a -1 charge
describe the reactivity of the halogens
less reactive as it goes down the group
why is it less reactive as we go down group 7 (halogens)
harder to gain electron as we go down the group.
greater distance between nucleus and outer electrons, more shielding from other electrons so the attraction between nucleus and outer electrons are decreased.
describe the displacement of halogens
a more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt
what are the properties of alkali metals
- soft metals
- relatively low melting points
- low density
- react rapidly with oxygen, chlorine and water
- form ions with a +1 charge
what are the properties of transition elements
- hard and strong metals
- high melting points (except mercury which is liquid at room temp)
- high density
- less reactive that group 1 (alkali) metals
- form ions with different charges
- form coloured compounds
- useful as catalysts
