1: Atomic Structure and the Periodic Table Flashcards
describe how compounds, how they are formed, and how they are separated.
they’re formed from elements by chemical reactions and contain two or more elements chemically combined in fixed proportions. they can only be separated into elements by chemical reactions.
what do chemical reactions involve?
they always involve the formation of one or more
new substances; often involve a detectable energy change
what are diatomic molecules and what are the homonuclear ones?
they’re molecules composed of only two atoms, of the same or different chemical elements
iodine, bromine, chlorine, fluorine, oxygen, nitrogen, hydrogen
what are mixtures?
consists of two or more elements or compounds not
chemically combined together - chemical properties of each substance in the mixture are unchanged.
list the ways mixtures can be separated.
can be separated by physical processes such as filtration, crystallisation, simple distillation, fractional distillation and chromatography- do not involve chemical reactions and no new substances are made
describe how you would separate a mixture by filtration.
used for separating an insoluble solid from a liquid
put filter paper in a filter funnel above beaker; pour the mixture of insoluble solid and liquid into the filter funnel; liquid particles are small enough to pass through the filter paper as a filtrate; solid particles are too large to pass through the filter paper and stay behind as a residue.
describe how you would separate a mixture by crystallisation.
used to separate a soluble solid from a liquid
place the solution in an evaporating basin and heat with a Bunsen burner; volume of the solution will decreased because some of the solvent has evaporated; solid particles will begin to form in the basin; once all the solvent has evaporated, solid crystals will be left behind.
describe how you would separate a mixture by simple distillation.
used for separating the solvent from a solution
solution is heated; solvent begins to evaporate and its vapours rise; vapour passes into the condenser, where it cools and condenses; liquid solvent drips into a beaker placed under condenser; once all the solvent has evaporated from the solution, the solute will be left behind.
describe how you would separate a mixture by fractional distillation.
used for separating a liquid from a mixture of two or more liquids
instead of having only one condenser, fractional distillation uses a column with several condensers placed at different heights; distillation column is hotter at the bottom and colder at the bottom; substances w higher boiling points will condense at the bottom of the column; substances w lower boiling points will condense at the top of the column
describe how you would separate a mixture by chromatography.
used for separating dissolved substances from one another e.g inks, food colourings and plant dyes
draw a pencil line and place spots of ink/plant dye etc. on it; fill a container of solvent, such as water/ethanol; lower the paper into the solvent; solvent travels up through the paper, taking some of the coloured substances with it; as the solvent continues to travel up the paper, the different coloured substances spread apart.
what was the earliest model/theory of the atom
they were thought to be indivisible, little spheres (John Dalton, 1803)
what is the plum pudding model?
J J Thomson discovered the electron; which led to creation of p. p. model - the atom is a ball of positive charge with negative electrons embedded in it
what is the nuclear model / alpha particle model?
1909, Ernest Rutherford fired positively charged alpha particles at thin gold foil; most alpha particles went straight through the foil; a few were scattered in different directions; led to conc. mass of an atom was concentrated at the nucleus; the nucleus was positively charged. nuclear model replaced the plum pudding model
how did Niels Bohr adapt the nuclear model?
suggested that electrons orbit the nucleus at specific distances; theoretical calculations of Bohr agreed with experimental observations.
how did Bohr’s model become adapted?
later experiments => nucleus contain smaller particles which had the same amount of positive charge - protons
how was the neutron discovered?
experimental work of James Chadwick in 1932 showed existence of neutrons within the nucleus, leading to another development of atomic model, which we use now
what is the relative mass and relative charge of a proton?
mass = 1; relative charge = +1
what is the relative mass and relative charge of a neutron?
mass = 1; relative charge = 0
what is the relative mass and relative charge of a electron?
mass = negligible; relative charge = -1
why do atoms have no overall charge?
the number of protons = the number of electrons
what is an isotope?
atoms that have the same proton number, but different neutron number
how do you calculate the Ar (relative atomic mass)?
Ar = total mass of atoms / total number of atoms
how are elements arranged in the periodic table?
all elements in a group have the same number of outer electrons - so similar chemical properties; number of shells = period number
describe the early attempts to classify elements.
tried to classify the elements by arranging them in order of their atomic weights; early periodic tables were incomplete - many elements unknown - and some elements were placed in inappropriate groups if the strict order of atomic weights was followed
describe how Mendeleev managed to help the development of the periodic table.
arranged the elements in order of increasing atomic weights; also took into account the properties of the elements and their compounds - showed elements with similar chem. properties lined up in groups; left gaps for elements that he thought had not been discovered and in some places changed the order based on atomic weights (due to different chem. properties)
how was Mendeleev’s table proved reliable?
elements with properties predicted by Mendeleev were discovered and filled the gaps; existence of isotopes explained why the order based on atomic weights was not always correct
what kind of ions do metal react to form?
positive ions
what kind of ions do non-metals react to form?
negative ions
describe the properties of group 0 elements.
called the noble gases; unreactive/inert; do not easily form molecules - their atoms have stable arrangements of electrons; have eight electrons in their outer shell, (except for helium, has two); boiling points increase with increasing relative atomic mass (going down the group)
why do the boiling points of noble gases increase going down the group?
atoms become larger; intermolecular forces between atoms become stronger; more energy needed to over these forces
describe the properties of group 1 elements (alkali metals).
single electron in their outer shell; form positive ions; are soft (they can be cut with a knife); have relatively low melting points; have low densities; reactivity increases going down group
what happens when lithium is added to water? (observation)
fizzes steadily; slowly becomes smaller until it disappears; moves slowly across surface of water
what happens when sodium is added to water? (observation)
fizzes rapidly; dissolves in water; quickly moves across surface of water
what happens when potassium is added to water? (observation)
burns violently with sparks and a lilac flame; quickly dissolves rapidly, often with a small explosion; rapidly moves across surface of water
describe alkali metals’ reaction w oxygen.
reacts to form metal oxides; at room temp. oxygen only reacts w surface of metal; burns vigorously when heated and placed in a jar of oxygen; reactions become more vigorous going down group
describe alkali metals’ reaction w chlorine.
react vigorously to form chlorides; at room temp. they’re white solids; dissolve in water to form colourless solutions; reactions become more vigorous going down group
why does reactivity increase going down group 1?
atoms become larger; outer electron is therefore further away from the nucleus; the force of attraction between the nucleus and the outer electron decreases; electron is lost more easily
describe the properties of group 7 elements (halogens).
simple molecules - molecules made of pairs of atoms joined by a single covalent bond; the further down the group an element is the higher its relative molecular mass, melting and boiling point
why do the melting and boiling points increase going down group 7?
molecules become larger; intermolecular forces become stronger; more energy is needed to overcome these forces
what do halogens react w metals to form?
salts - ionic compound
what do halogens react w hydrogen (non-metal) to form?
hydrogen halide-
why does reactivity decrease down group 7?
atoms become larger; outer electron is therefore further away from the nucleus; the force of attraction between the nucleus and the outer shell decreases; harder to gain electron; becomes less reactive
how do halogens displace other halogens?
more reactive halogen can displace less reactive halogen from solutions of its salts
describe the physical properties of all metals. (2)
conduct electricity in the solid and liquid states; shiny when freshly cut
what typical physical properties do only transition metals have (group 1 don’t) (4)?
higher melting points; higher densities; greater strength; greater hardness
describe the differences in chemical properties between group 1 metals and transition metals (reactions w oxygen, cold water and halogens).
group 1 react quickly w oxygen, most t metal react slowly, or not at all; group 1 react vigorously w cold water, most t metal react slowly, or not at all; iron reacts w water and oxygen to form rust; group 1 react vigorously w halogens
describe typical properties of transition metals.
form differently charged ions (e.g. Fe2+, Fe3+) ; form coloured compounds; they are useful as catalysts - they’re unreactive so can be reclaimed/reused, can form ions w different charges
