Karteikarten
Atomic Structure and The Periodic Table
Karten in diesem Stapel (33)
- 1AtomAll substances are made of atoms. An atom is the
smallest part of an element that can exist.
Atoms of each element are represented by a chemical
symbol - 2CompoundsSome elements combine through chemical
reactions to form compounds.
Compounds are made from two or more
different elements (types of atoms) combined
together in fixed proportions and can be
represented by formulae using the symbols of
the atoms from which they were formed
Compounds have different properties from the
elements they are made from.
Compounds can only be separated into elements
by chemical reactions. - 3Elements and The Periodic TableAn element is a substance with only one type of atom.
Elements are listed in the periodic table. There are about 100
different elements.
Elements can be classified as metal or non-metal depending
on their properties.
The columns in the periodic table are called groups and
contain similar elements.
The rows in the periodic table are called periods. Elements
show a gradual change in properties across a period - 4MixturesA mixture consists of two or more elements or compounds not
chemically combined together.
The chemical properties of each substance in the mixture are
unchanged. - 5Separating TechniquesMixtures can be separated by physical processes
such as filtration, crystallisation, simple distillation,
fractional distillation and chromatography. These
physical processes do not involve chemical
reactions. - 6Simple DistillationType of mixture separated:
soluble solid dissolved in a liquid (usually water) e.g.
salty water
explanation:
liquid boils off and condenses in the condenser. The
thermometer will read the boiling point of the pure
liquid. - 7Crystallisation/ EvaporationTo separate a soluble solid from a (nonflammable)
liquid we use evaporation. If we
want to create hydrated salt crystals then do
not evaporate all the water from the mixture - 8Fractional DistillationType of mixture separated:
Soluble liquids with different boiling points e.g. crude oil
The fractionating column has a temperature gradient and
is hotter at the bottom than at the top
Explanation: When a mixture of soluble liquids is heated all
liquids are evaporated. The liquid with the lower boiling point,
however, forms the greatest percentage of vapour. As the
vapour moves up the fractionating column it becomes more
rich with the component that has the lowest boiling point. This
is due to the vapour mixture condensing and evaporating as it
moves up the column.
A thermometer measures the temperature of the fractions
before they condense. The liquid with the lowest boiling point
will be the first 'fraction' to collect. - 9FiltrationType of mixture separated:
insoluble solid suspended in a liquid
(usually water) e.g. sand and water.
Filter
funnel
Filter
paper residue
filtrate
Filtration
Explanation:
The insoluble solid (called residue) gets caught in
the filter paper, because the particles are too big
to fit through the holes in the paper.
The filtrate is the substance that comes through
the filter paper. - 10Plum Pudding ModelThe discovery of the electron led to
the plum-pudding model of the
atom. The plum-pudding model
suggested that the atom was a ball
of positive charge with negative
electrons embedded in it - 11Nuclear ModelThe results from the Rutherford and Marsden’s alpha scattering experiments
led to the plum-pudding model being replaced by the nuclear model.
Neils Bohr adapted the nuclear model by suggesting that electrons orbit the
nucleus at specific distances. The theoretical calculations of Bohr agreed with
experimental observations - 12The History of the Development of the AtomLater experiments led to the idea that the positive
charge of any nucleus could be subdivided into a whole
number of smaller particles, each particle having the
same amount of positive charge. The name proton was
given to these particles
The experimental work of James Chadwick provided the
evidence to show the existence of neutrons within the
nucleus. This was about 20 years after the nucleus
became an accepted scientific idea. - 13Sub-Atomic ParticlesProton - 1 /+1
Neutron - 1 /0
Electron - Very small /-1 - 14The AtomAtoms have a small central nucleus made
up of protons and neutrons around which
there are electrons.
In an atom, the number of electrons is
equal to the number of protons in the
nucleus. Atoms have no overall electrical
charge.
All atoms of a particular element have the
same number of protons.
Atoms of different elements have different
numbers of protons.
Most of the mass of an atom is in the nucleus
The total number of protons and neutrons in
an atom is called its mass number - 15Size of an AtomAtoms are very small, having a radius of about
0.1 nm (1x 10-10 m).
The radius of a nucleus is less than 1/10 000 of
that of the atom (about 1 x 10-14 m). - 16Key NotesThe number of protons in an atom is called its atomic number
(proton number). Atoms are arranged in the modern periodic
table in order of their atomic number (proton number).
To work out the number of neutrons in an atom subtract the
atomic number from the mass number - 17IsotopesAtoms of the same element can have different numbers of neutrons; these atoms are called isotopes of that element.
Isotopes of an element have the same chemical properties because they have the same electronic structure - 18Calculating Relative Atomic MassThe relative atomic mass of an element is an average value that takes account of
the abundance of the isotopes of the element. - 19EquationR.A.M = Σ (isotopic mass x % abundance)
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100 - 20Electronic StructureElectrons occupy particular energy levels. Each electron in an
atom is at a particular energy level.
The electrons in an atom occupy the lowest available energy
levels .
The first energy level can hold a maximum of two electrons,
the 2nd and 3rd can hold up to 8. (not really true for 3rd ).
Elements in the same group in the periodic table have the
same number of electrons in the highest energy levels (outer
electrons) and this gives them similar properties. E.g. group 1
elements all have 1 electron in their outer shell.
The elements in Group 0 of the periodic table are called the
noble gases. They are unreactive because their atoms have
stable arrangements of electrons.
Elements in the same period have the same
number of energy levels. - 21The Modern Periodic TableThe elements in the periodic table are arranged in
order of atomic (proton) number and so that elements
with similar properties are in columns, known as
groups.
The table is called a periodic table because similar
properties occur at regular intervals.
Elements in the same group in the periodic table have
the same number of electrons in their outer shell
(outer electrons) and this gives them similar chemical
properties
The modern periodic table can be seen as an
arrangement of the elements in terms of their
electronic structures.
o atomic number gives number of protons or
electrons
o Elements in the same Group have the same
number of electrons in their highest occupied
energy level (outer shell). (This explains
similar reactivity)
o Elements in the same period have the same
number of shells
o As you go down a group the number of shells
increases. - 22The Early Periodic TableBefore the discovery of protons, neutrons and electrons,
scientists attempted to classify the elements by arranging them
in order of their atomic weights.
The early periodic tables were incomplete and some elements
were placed in inappropriate groups if the strict order of
atomic weights was followed.
Knowledge of isotopes made it possible to explain why the
order based on atomic weights was not always correct. - 23Key Notes on the Early Periodic TableMendeleev – leaving gaps
Mendeleev overcame some of the problems by
leaving gaps for elements that he thought had not
been discovered and in some places changed the
order based on atomic weights.
Elements with properties predicted by Mendeleev
were discovered and filled the gaps. - 24Metals and Non-MetalsElements that react to form positive ions are metals.
Elements that do not form positive ions are non-metals.
(note- hydrogen is an exception to this rule)
The majority of elements are metals. Metals are
found to the left and towards the bottom of the
periodic table. Non- metals are found towards
the right and top of the periodic table. - 25Noble GasesThe elements in Group 0 of the periodic table are called the noble gases. They are unreactive and do not easily form
molecules because their atoms have stable arrangements of electrons.
The noble gases have eight electrons in their outer energy level, except for helium, which has only two electrons
The boiling points of the noble gases increase with increasing relative atomic mass (going down the group) - 26Group 1- The Alkali MetalsThe elements in Group 1 of the periodic table
o all have 1 electron in their highest
energy level
o are metals with low density (the first
three elements in the Group are less
dense than water)
o are stored under oil to prevent them
from reacting with oxygen or water - 27Reactions of Group 1o Group 1 metals react in a similar way as
they all have 1 electron in their outer shell
o react with non-metals to form ionic
compounds in which the metal ion carries a
charge of + 1. The compounds are white
solids which dissolve in water to form
colourless solutions
o e.g. 2 Na + Cl2 -> 2NaCl - 28Reaction with Watero Group 1 metals react with water releasing
hydrogen and form hydroxides which
dissolve in water to give alkaline solutions.
(this is why they are known as alkali metals)
o They react vigorously with water fizzing and
moving around on the surface of the water
o e.g. 2Na + 2H2O -> 2NaOH + H2 - 29Increasing Reactivity Down the GroupIn Group 1, the further down the group an
element is the more reactive it becomes as the
atoms get larger the outer electrons are further
from the nucleus and thus less attracted to the
nucleus and so can more easily lose electrons - 30Group 7- The HalogensThe elements in Group 7 of the periodic table :
o all have 7 electrons in their highest energy level
o have coloured vapours
o consist of molecules which are made up of pairs of atoms (Cl2,Br2,I2)
o form ionic salts with metals in which the chloride, bromide or iodide ion (halide
ion) carries a charge of -1
o form molecular (simple covalent) compounds with other non-metallic elements. - 31Trends in Group 7In Group 7, the further down the group an element is:
o the higher its relative molecular mass
o the higher its melting point and boiling point.
o the less reactive the element as the atoms get bigger, electrons are further from
nucleus and less strongly attracted so it can less easily gain electrons. - 32Displacement ReactionsA more reactive halogen can displace a less reactive halogen
from an aqueous solution of its salt. - 33Transition MetalsIn the periodic table between Groups 2 and 3 is a block of elements known as the transition elements.
These elements are all metals.
Compared with the elements in Group 1, transition elements:
• have higher melting points (except for mercury) and higher densities
• are stronger and harder
• are much less reactive and so do not react as vigorously with water or oxygen.
Many transition elements
• have ions with different charges,
• form coloured compounds
• are useful as catalysts.
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- Flashcards made from a GCSE AQA revision guide
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