Atomic Structure & the Perioic Table Flashcards
Simple Model of Atom
All substances are made of tiny particles of matter called
atoms which are the building blocks of all matter
Each atom is made of subatomic particles called
protons, neutrons, and electrons
The protons and neutrons are located at the centre of the atom, which is called
the nucleus
The electrons move very fast around the nucleus in orbital paths called
shells
The mass of the electron is
negligible, hence the mass of an atom is contained within the nucleus where the protons and neutrons are located
a substance made of atoms that all contain the same number of protons and cannot be split into anything simpler.
element
Elements take part in chemical reactions in which new substances are made in processes that most often involve an
energy change
In these reactions atoms combine together in fixed ratios that will give them
full outer shells of electrons, often producing compounds
A compound is a pure substance made up of two or more elements chemically …
combined and which cannot be separated by physical means
number of compounds is ///
unlimuted
Ionic compounds contain
metal and non-metal elements joined together as particles called ions
The non-metal element always takes on the name ending
‘– ide’ unless oxygen is also present,
For example, PbS is called lead sulfide and MgCl2 is called magnesium chloride
When oxygen is present the name ending is usually
‘-ate’
For example, CuSO4 is copper sulphate, KClO3 is potassium chlorate and Na2CO3 is sodium carbonate
The ending ‘-ite’ will always have
less oxygen than ‘-ate’
H2SO4 is
sulfuric acid
NH3
ammonia
CH4
methane
HCl
hydrochloric acid (or hydrogen chloride if it is a gas)
C6H12O6
glucose
C2H5OH
ethanol
HNO3
nitric acid
The reactants are those substances on the
left-hand side of the arrow and can be thought of as the chemical ingredients of the reaction
The products are the new substances which are on the
right-hand side of the arrow
The arrow (which is spoken as “goes to” or “produces”) implies the conversion of reactants into products
Reaction conditions or the name of a
catalyst (a substance added to make a reaction go faster) can be written above the arrow
An example is the reaction of sodium hydroxide (a base) and hydrochloric acid producing sodium chloride (common table salt) and water:
Sodium hydroxide + hydrochloric acid ⟶ sodium chloride + water
S + O2 →
SO2
This equation shows that one atom of sulfur (S) reacts with one molecule of oxygen (O2) to make one molecule of sulfur dioxide (SO2)
Nothing created - nothing
destroyed
New substances are made during chemical reactions
However, the same atoms are always present before and after reaction
They have just joined up in different ways
Atoms cannot be created or destroyed, so if they exist in the reactants then they absolutely must be in the products!
Because of this the total mass of reactants is always equal to the total mass of products
This idea is known as the Law of Conservation of Mass
The Law of Conservation of Mass enables us to
balance chemical equations, since no atoms can be lost or created
You should be able to:
Write word equations for reactions outlined in these notes
Write formulae and balanced chemical equations for the reactions in these notes
Pb2+ + 2e- →
Pb
2Br- →
Br2 + 2e-
Half equations are used to show what happens to the
electrons in reactions where atoms, molecules or ions are gaining or losing electrons
Ionic equations are used to indicate what happens to ions during reactions
They help to simplify
complicated processes where many substances are present, but only certain ions are actually reacting with each other
For example, we can use ionic equations to show what happens when an acid neutralizes and an alkali:
HCl + NaOH → NaCl + H2O
Written out as an ionic equation would be
H+ + OH- → H2O
This is because sodium and chloride ions were present at the beginning and also at the end of the reaction, so they are unchanged
Ions which are present but do not take part in reactions are called spectator ions
Mixtures can contain elements and
/ or compounds
Each constituent of the mixture retains its
chemical properties
4The parts of a mixture are not chemically bonded together and so they can be separated by
physical means
The choice of the method of separation depends on the nature of the substances being separated
All methods rely on there being a difference in a physical property such as the boiling point or solubility, between the substances being separated
Filtration
Used to separate an
undissolved solid from a mixture of the solid and a liquid / solution ( e.g., sand from a mixture of sand and water)
Centrifugation and decanting can also be used for this mixture
A piece of filter paper is placed in a filter funnel above a beaker
A mixture of insoluble solid and liquid is poured into the filter funnel
The filter paper will only allow small liquid particles to pass through as filtrate
Solid particles are too large to pass through the filter paper so will stay behind as a residue
Crystallisation
Used to separate a
dissolved solid from a solution, when the solid is much more soluble in hot solvent than in cold (e.g., copper sulphate from a solution of copper (II) sulphate in water)
To test if the solution is saturated a clean, dry, cold glass rod is dipped into the solution
If the solution is saturated, crystals will form on the glass rod
The saturated solution is then allowed to cool slowly
Crystals begin to grow as solids come out of solution due to decreasing solubility
The crystals are collected by filtering the solution, they are washed with cold distilled water to remove impurities and are then allowed to dry
Simple Distillation
This is used to separate a
a liquid and soluble solid from a solution (e.g., water from a solution of salt water) or a pure liquid from a mixture of liquids
The solution is heated and a liquid evaporates producing a vapour which rises through the neck of the round-bottomed flask (e.g. for saltwater, this would be water boiling at 100 oC)
The vapour passes through the condenser, where it cools and condenses, turning into the pure liquid that is collected in a beaker
After all the liquid is evaporated from the solution, only the solid solute will be left behind
Fractional Distillation
This is used to separate two or more liquids that are
miscible with one another (e.g., ethanol and water from a mixture of the two)
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
For water and ethanol
Ethanol has a boiling point of 78 ºC and water of 100 ºC
The mixture is heated until it reaches 78 ºC, at which point the ethanol boils and distills out of the mixture and condenses into the beaker
When the temperature starts to increase to 100 ºC heating should be stopped. Water and ethanol are now separated
Paper Chromatography
This technique is used to separate substances that have
different solubilities in a given solvent (e.g., different coloured inks that have been mixed to make black ink)
A pencil line is drawn on chromatography paper and spots of the
sample are placed on it. Pencil is used for this as ink would run into the chromatogram along with the samples4
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
Different substances have different solubilities so will travel at different rates, causing the substances
to spread apart
Those substances with higher solubility will travel further than the others
This will show the different components of the ink / dye
If two or more substances are the same, they will produce ________ chromatogram
identical
If the substance is a mixture, it will separate on the paper to show all the different components as
separete spots
An impure substance will show up with more than one spot, a pure substance should only show up
with one spot
In 1803, John Dalton presented his atomic theory based on three key ideas:
Matter is made of atoms which are tiny particles that cannot be created, destroyed, or divided
Atoms of the same element are identical, and atoms of different elements are different
Different atoms combine together to form new substances
At the time, the theory was correct but as science developed
some parts of Dalton’s theory were disproved
This is a fundamental feature of science: new experimental evidence may lead to a scientific model being changed or replaced
The Plum Pudding Model
In 1897, physicist J.J. Thomson discovered the
electrone
Using a cathode-ray tube
he conducted an experiment which identified the electron as a negatively charged subatomic particle, hence proving that atoms are divisible
the plum pudding model deplicated
negative electrons spread throughout soft globules of positively charged material
Rutherford shot a beam of positively charged particles at a thin sheet of gold foil and based on the plum pudding model, expected the particles to pass through the
foil because the positive charge of the nucleus was thought to be evenly spread out
The results of Rutherford’s scattering experiments
did not support the idea that atoms were as described in the plum pudding model, so the model had to be changed
In Rutherford’s model, the atom consists mainly of
empty space with the nucleus at the centre and the electrons orbiting in paths around the nucleus
This model was known as the nuclear model of the atom
In the plum pudding model, atoms were described as being made from electrons embedded within a positive sphere, whereas in the nuclear model the nucleus is a
a positive structure at the centre of the atom, with negative (and much smaller) electrons ‘orbiting’ around the outside of it
In 1913, Niels Bohr further developed the nuclear model by proposing that electrons
orbit the nucleus in fixed shells or orbitals located at set distances from the nucleus
Each orbital has a different energy associated with it, with the higher energy orbitals being located
further away from the nucleus
The Bohr Model solved the question of why the atom does not collapse inwards due to the
attraction between the positive nucleus and negative electrons circling the nucleus
the subatomic particles that make up atoms
Protons, neutrons and electrons
Atoms are extremely small with a radius of about
1 x 10-10 metres or 0.1 nanometres
Electrons have a much smaller mass than
protons and neutrons (1 proton has the same mass of around 1840 electrons) and move in the space outside the nucleus in orbits
Electrons can be
lost, gained, or shared during chemical processes but the proton number of an atom does not change in a chemical reaction
Isotopes are atoms of the
same element that contain the same number of protons and electrons but a different number of neutrons
Isotopes display the same
chemical characteristics
This is because they have the same number of electrons in their outer shells, and this is what determines their chemistry
The difference between isotopes is
the neutrons which are neutral particles within the nucleus and add mass only
