1- ATOMIC STRUCTURE AND PERIODIC TABLE Flashcards
how big is the radius of an atom
0.1 nanometers (1 x 10^-10m)
explain properties of the nucleus in atoms
-middle of the atom
-contains protons and neutrons
- has radius of around 1x10^-14
which is around 1/10,000 of the radius of an atom
- has a positive charge due to protons
-almost whole mass of atom is concentrated in the nucleus
explain properties of electrons in atoms
moves around the nucleus in electron shells
negatively charged and tiny but cover a lot of space
volume of their orbits determines the size of atoms
electrons have virtually no mass
state the relative mass and charge for each subatomic particle
relative mass charge
proton has 1 +1
neutron 1 0
electron 0 -1
why do atoms have no charge overall
same number of protons and electrons
charge of electrons is same size as the charge on the protons so charges cancel out
why are charges in ions different
number of protons do not equal the number of electrons
so it does have an overall charge
e.g. an ion with a 2- charge
(has 2 more electrons than protons)
atomic number
tells you how many protons ther are
at the bottom left of the symbol
mass number
total number of protons and neutrons
top left of symbol
to get number of neutrons
subtract atomic number from mass number
explain how elements consist of atoms with the same atomic number
number of protons in nucleus determines what type of atom it is
e.g. atom with 1 proton in its nucleus is hydrogen
atoms with 2 protons is helium
all atoms of a particular element have same number of protons
different elements have atoms with different numbers of protons
isotopes
elements can exist as a number of different isotopes
different forms of the same element
same number of protons
different number of neutrons
so same atomic number
different mass numbers
e.g. carbon 12/ carbon 13
explain relative atomic mass
how do you work it out
referring to the element as a whole
=average mass of different masses and abundances of all the isotopes that make up the element
Ar= sum of (isotope abundance x
isotope mass number)
——————————
sum of abundances of
all the isotopes
practice question- working out relative atomic mass
copper has 2 stable isotopes
cu-63 has abundance of 69.2%
cu-65 has abundance of 30.8%
calculate relative atomic mass
(69.2 x 63) + (30.8 x 65)
___________________
69.2 + 30.8
=
4359.6 + 2002 /100= 6361.6/100 = 63.616= 63.6
what
are compounds formed
when elements react, atoms combine with other atoms to form compounds
compounds are substances formed from 2 or more elements= the atoms of each are in fixed proportions throughout the compound and held together by chemical bonds
how are compounds formed
when elements react, atoms combine with other atoms to form compounds
compounds are substances formed from 2 or more elements= the atoms of each are in fixed proportions throughout the compound and held together by chemical bonds
making bonds involve giving away giving/taking/sharing electrons= only the electrons are involved: the nuclei the atoms arent affected
how can you separate the original elements of a compound out again
with a chemical reaction
what does a compound made from metals and non metals consist of…
explain ionic bonding
ions
metal atoms lose electrons to form positive ions and non metal atoms gain electrons to form negative ions
=opposite charges of the ions means they are strongly attracted to each other =IONIC BONDING
examples of compounds ionically bonded-
sodium chloride, magnesium oxide,calcium oxide
explain covalent bonding
a compound formed from non metals consist of molecules
each atom shares an electrom with another atom
e.g. hydrogen chloride gas, carbon monoxide, water
explain properties of compounds are different from properties of original elements
e.g.
if iron (magnetic metal) and sulfur (yellow powder) react, compound formed (iron sulfide ) is a dull grey solid and doesnt behave in the way iron or sulfur does
explain how brackets work in a chemical formula
Ca(OH)2
number outside bracket applies to everything only inside the bracket
so
1 calcium
2 oxygen atoms
2 hydrogen atoms
chemical formula for carbon dioxide
ammonia
water
sodium chloride
carbon monoxide
hydrochloric acid
calcium chloride
sodium carbonate
sulfuric acid
CO2
NH3
H2O
NaCl
CO
HCl
CaCl2
Na2CO3
H2SO4
why can mixtures be easily separated
no chemical bonds between the different parts of a mixture
parts of a mixture can be an element or compound
so can be separated out by physical methods e.g. filtration,crystallisation,simple distillation,fractional distillation,chromatography
what is air a mixture of
mixture of gases
mainly nitrogen, oxygen, carbon dioxide and argon
these gases can all be separated out fairly easily
what is crude oil a mixture of
different length hydrocarbon molecules
what are the properties of a mixture
its just a mixture of properties of the separate parts
chemical properties of a substance are not affected by it being part of a mixture
e.g. mix of iron and sulfur powder has properties of both iron and sulfur
practical
explain paper chromatography
separating different dyes in an ink
1) draw a line near the bottom of a sheet of filter paper(use pencil bc they are insoluble and wont dissolve in solvent)
2) add spot of ink to line and place sheet in a beaker of solvent e.g. water
3) solvent depends on what is being tested (some compounds dissolve well in water, others in ethanol)
4) make sure ink isnt touching solvent as you dont want it to dissolve
5) place lid on top of container to stop solvent from evaporating
6) solvent seeps up the paper, carries ink with it
7) each different dye in ink will move up paper at different rate so dyes will separate out, each dye will form a spot in a different place- 1 spot per dye in ink
8) if any of the dyes are insoluble in solvent theyll stay on baseline
9) when solvent has nearly reached top of paper =take paper out of beaker and leave it to dry
end result is a pattern of spots called chromatogram
when is filtration used
used if product is an insoluble solid that needs to be separated from a liquid reaction mixture
can be used in purification as well
e.g. solid impurities in the reaction mixture can be separated out using filtration
how can you separate soluble solids from solutions using evaporation
evaporation
1-pour solution into an evaporating dish
2-slowly heat solution, solvent will evaporate and solution will get more concentrated then crystals will start to form
3-keep heating the evaporating dish until all is left is dry crystals
you can only use this method if the salt doesnt decompose when it is heated
if it does decompose you need to use crystallisation
how can you separate soluble solids from solution using crystallisation
1- pour solution into evaporating dish and gently heat solution, some solvent will evaporate and solution will get more concentrated
2- once some of the solvent has evaporated or when you see crystals start to form (point of crystallisation) remove dish from heat and leave solution to cool
3- salt should start to form crystals as it becomes insoluble in the cold, highly concentrated solution
4- filter the crystals out of the solution and leave them in a warm place to dry (you could use a drying over or a desiccator)
how can you separate soluble solids from solution using crystallisation
1- pour solution into evaporating dish and gently heat solution, some solvent will evaporate and solution will get more concentrated
2- once some of the solvent has evaporated or when you see crystals start to form (point of crystallisation) remove dish from heat and leave solution to cool
3- salt should start to form crystals as it becomes insoluble in the cold, highly concentrated solution
4- filter the crystals out of the solution and leave them in a warm place to dry (you could use a drying over or a desiccator)
how can filtration and crystallisation be used to separate rock salt
rock salt is simply a mixture of salt and sand(spread it on roads in winter)
salt and sand are both compounds but salt dissolves in water and sand does not
difference in physical properties helps separate them
1- grind mixture to make sure salt crystals are small so dissolves easily
2- put mixture in water & stir, salt will dissolve but sand wont
3- filter mixture, grains of sand wont fit through tiny holes in filter paper so they collect on the paper instead
4-salt passes through the filter paper as part of solution
5- evaporate water from salt so it forms dry crystals
explain simple distillation
its used for separating a liquid out from a solution
1-solution is heated, part of solution with lowest boiling point evaporates first
vapour is then cooled, condenses and collected
2-rest of solution is left behind in the flask
3- you can use this to get pure water from seawater as water evaporates and is condensed and collected and you end up with salt in a flask
what is the problem with simple distillation
you can only use it to separate things with very different boiling points
if the temperature goes higher than the boiling point of the substance with the higher boiling point, they will mix again
if you have a mixture of liquids with similar boiling points you need to use fractional distillation
explain fractional distillation
to separate a mixture of liquids
1- put mixture in a flask and stick a fractioning column on top then heat it
2- different liquids will all have different boiling points so they will evaporate at different temperatures
3- liquid with lowest boiling point evaporates first, when temperature on thermometer matches boiling point of liquid it will reach the top of the column
4-liquids with higher boiling points might also start to evaporate but column is cooler towards top so they will only get part of the way up before condensing and running back down to the flash
5- when first liquid has been collected, you raise temperature until next one reaches the top
history of atom p1
how did john dalton describe atoms at the beginning of the 19th century
solid spheres
different spheres made of different elements
history of atom p2
how did jj thomson describe atoms in 1897
concluded from his experiments that atoms were not solid spheres
his measurements of charge and mass showed that an atom must contain even smaller negatively charged particles- electrons
new theory was plum pudding model= ball of positive charge with electrons stuck in it
history of atom p3
what did ernest rutherford say in 1909
alpha scattering experiment
fired positively charged alpha particles at thin sheet of gold, =most particles went straight through gold sheet, some deflected more than expected, small number deflected backwards
so plum pudding was not right
this explained the nuclear model of the atom,
there was instead a positively charged nucleus in the middle where most of the mass was concentrated, negative electrons surrounding the nucleus so most of atom was empty space
when alpha particles came near concentrated positive charge of the nucleus, they were deflected
if they were fired directly at the nucleus, they were deflected backwards otherwise they passed through empty space
history of atom p4
explain bohrs nuclear model
suggested all the electrons were contained in shells
the electrons orbit the nucleus in fixed shells and arent anywhere inbetween, each shell is a fixed distance from the nucleus
his theory of atomic structure was supported by many experiments was supported by experiemnts and explained observations made by scientists
how was existence of protons found
further experiments by rutherford and others showed that nucleus can be divided into smaller particles which each have same charge as a hydrogen nucleus = particles named protons
history of atom p5
what did james chadwick discover around 20 years later
he carried out an experiment which provided evidence for neutral particles in the nucleus called neutrons
discovey of neutrons resulted in model of the atom which is pretty close to the nuclear model
electron shell rules
electrons always occupy shells (energy levels)
lowest energy level is always filled first
only 2 electrons on first shell
8 on 2nd and 3rd shell
atoms are always trying to get a full shell
e.g. noble gases = group 0
so in most atoms the outer shell is not full and this makes the atom want to react to fill it
how were elements arranged in the early 1800s
explain how the early periodic table was arranged
arranged by atomic mass
= physical and chemical properties
= their relative atomic mass
= the only thing they could measure was relative atomic mass so known elements arranged in order of atomic mass
then periodic pattern was noticed in properties of elements
early periodic table not complete, some elements placed in wrong group bc elements placed in order of relative atomic mass and not properties
how did dmitri mendeleev arrange the periodic table in 1869
left gaps and predicted new elements
he took 50 known elements and arranged them in his table with gaps
he put elements in order of atomic mass but did switch the order if the properties meant it should be changed
eg with Te and I - iodine has smaller relative atomic mass but placed after terellium as it has similar properties to the elements in that group
gaps left in table to make sure elements with similar properties stayed in same groups, gaps indicated existence of undiscovered elements , allowed mendeleev to predict what their properties might be
when found they fitted the pattern,helped confirm his idea
how did the discovery of isotopes in the early 20th century confirm mendeleev was correct
he was correct not to place elements in a strict order of atomic mass but to also take in account their properties
isotopes of the same element have different atomic masses but same chemical properties so occupy same position on periodic table
in periodic table, what are elements laid out in order of
increasing atomic (proton) number
so repeating patterns in the properties if elements
properties arre said to occur periodically
metals are found to the left
non metals are found to the right
what do columns in the periodic table show
elements with similar properties form columns
vertical columns are called groups
group number tells you how many electrons are in outer shell
(but for group 0 there are 2 electrons on outer shell)
if you know properties of 1 element you can predict properties of other elements in group
e.g. group 1 all metals and react in similar ways
also shows trends in reactivity
how does reactivity of group 1 change as u go down the group
elements react more vigourously as you go down the group
how does reactivity of group 7 change as u go down the group
reactivity decreases as you go down the group
what do rows in periodic table show
each new period represents another full shell of electrons
explain the elements= non metals and metals in the periodic table
they can form positive ions when they react
towards the bottom and left of the periodic table
most elements in periodic table are metals
non metals are at far right and top of periodic table
they dont generally form positive ions when reacting
how does the electronic structure of atoms affect how they will react = for metals
atoms generally react to form a full outer shell by losing/gaining/sharing electrons
metals to left of periodic table dont have many electrons to remove and metals near bottom have outer electrons that are far away from the nucleus so theres a weaker attraction so not much energy is needed to remove electrons so its easier for elements to react to form positive ions to form a full outer shell
how does electronic structure of non metals affect how they will react
forming positive ions is much more difficult
they have lots of electrons to remove to get a full outer shell or towards top where outer electrons are closer to nucleus to feel a stronger attraction
it is easier for them to share or gain electrons to get a full outer shell
all metals have metallic bonding causing them to have similar basic properties
what are these
explain the properties of metals
strong (hard to break) but can be bent or hammered into different shapes (malleable)
great at conducting heat and electricity
high boiling points and melting points
explain properties of nonmetals
dont have metallic bonding
dull looking
more brittle
arent always solids at room temperature
dont generally conduct electricity
often have low density
explain what transition metals are
in the centre of the periodic table
theyre typical metals, ‘proper metals’
good conductors of heat and electricity
very dense, strong and shiny
they can have more than one ion e.g. Cu can from Cu+ and Cu2+
Cobalt can form Co2+ and Co3+
transition metal ions are often coloured so compounds that contain them are colourful
e.g. potassium chromate is yellow, potassium manganate is purple
transition metal compounds make good catalysts e.g. nickel based catalyst is used in hydrogenation of alkenes & iron catalyst is used in Haber process to make ammonia
what are the alkali metals- group 1 metals
lithium sodium potassium rubidium caesium francium
why are group 1 metals very reactive
what are properties of group 1 metals-alkali metals
they all have one electron in their outer shell which makes the very reactive and they are more ready to lose that electron to become a positive ion in order to gain a full outer shell
this gives them similar properties
alkali metals are all soft and have a low density
what are trends for alkali metals as you go down the group
1- increasing reactivity= the outer electron is more easily lost as the attraction between the nucleus and electron decreases because the electron is further away from the nucleus the further down the group you go
2- lower melting and boiling points
3- higher relative atomic mass
what are trends for alkali metals as you go down the group
1- increasing reactivity= the outer electron is more easily lost as the attraction between the nucleus and electron decreases because the electron is further away from the nucleus the further down the group you go
2- lower melting and boiling points
3- higher relative atomic mass
what are trends for alkali metals as you go down the group
1- increasing reactivity= the outer electron is more easily lost as the attraction between the nucleus and electron decreases because the electron is further away from the nucleus the further down the group you go
2- lower melting and boiling points
3- higher relative atomic mass
how can alkali metals (group 1) form ionic compounds with non metals
group 1 metals dont need much energy to lose their 1 outer electron to form a full outer shell so they readily form 1+ ions
so its easy for them to lose their outer electron that they only ever react to form ionic compounds
these compounds are generally white solids that dissolve in water to form colour less solutions
how does group 1 alkali metals react in water
-reacts vigorously to produce hydrogen gas and metal hydroxides: salts that dissolve in water to produce alkaline solutions
- the more reactive(lower down the group) an alkali metal is the more violent the reaction is
- the amount of energy given out by the reaction increases down the group: the reaction with potassium releases enough energy to ignite hydrogen
e.g.
2Na + 2H2O => 2NaOH + H2
sodium + water => sodium hydroxide + hydrogen
how does group 1 alkali metals react with chlorine
they react vigorously when heated in chlorine gas to form white metal chloride salts
as you go down the group,reactivity increases so the reaction with chlorine becomes more vigorous
how does group 1 alkali metals react with oxygen
they react with oxygen to form a metal oxide
different types of oxides form depending on the group 1 metal
=lithium reacts to form lithium oxide (Li2O)
=sodium forms a mixture of sodium oxide(Na2O) and sodium peroxide (Na2O2)
=potassium forms mixture of potassium peroxide (K2O2) and potassium superoxide (KO2)
how do group 1 metals have different properties to transition metals
group 1 metals are much more reactive thn transition metals
they react more vigorously in water,oxygen or group 1 elements
G1 is less dense,strong,hard than the transition metals and have much lower melting points (e.g. manganese melts at 2000 degrees celsius, sodium melts at 98 degrees celsius)
name the halogens - group 7 elements
flourine
chlorine
bromine
iodine
astatine
explain the properties of individual group 7 elements- halogens
flourine is a very reactive poisonous yellow gas
chlorine is a fairly reactive poisonous dense green gas
bromine is dense poisonous red/brown volatile liquid
iodine is dark grey crystalline solid or purple vapour
all exists as molecules (pairs of atoms)
explain the trends of group 7 elements (halogens)
as you go down the group
it becomes less reactive(harder to gain extra electron because outer shell is further away from nucleus)
- higher melting and boiling points
-higher relative atmoic mass
they all react in similar ways as they all have 7 electrons on their outer shell
how can halogens form molecular compounds
halogen atoms share electrons via covalent bonding with other nonmetals to achieve full outer shell
e.g. HCl, PCl5, HF, CCI4 contain covalent bonds
the compounds that form when halogens react with non metals all have simple molecular structures
how can halogens form ionic bonds with metals
halogens form 1- ions called halides
(F-, Cl-, Br-, I-) when they bond with metals e.g. Na+Cl-, Fe3+Br-3
the compounds that form ionic sturctures
how can halogens form ionic bonds with metals
halogens form 1- ions called halides
(F-, Cl-, Br-, I-) when they bond with metals e.g. Na+Cl-, Fe3+Br-3
the compounds that form ionic sturctures
why do more reactive halogens displace less reactive ones
a displacement reaction occurs between a more reactive halogen and the salt of a less reactive one
e.g. chlorine can displace bromine and iodine from an aqueous solution of its salt(bromide or iodide)
bromine will also displace iodine because of the trend in reactivity
Cl 2(g) + 2Kl(aq) => I2 (aq)+ 2KCl(aq)
pale green brown
Cl2(g)+ 2KBr (aq)=> Br2(aq) + 2KCl(aq)
pale green orange
group 0 elements= noble gases name them
helium
neon
argon
krypton
xenon
radon
describe electronic structure of
group 0 =noble gases
they all have 8 electrons in their outer energy level apart from helium which has 2
giving them a full outer shell
as their outer shell us energetically stable they dont need to give up or gain electrons to become more stable
so they are more or less inert= dont react much#
they exist as monatomic gases (single atoms not bonded to each other)
all elements in group 0 are colourless gases at room temperature
as noble gases are inert theyre non flammable: they wont set on fire
explain trends for noble gases as you go down the group =group 0
boiling points of noble gases increase as you move down the group along with increasing relative atomic mass
increase in boiling point due to an increase in the number of electrons in each atom leading to greater intermolecular forces between them which need to be overcome
neon is a gas at 25 degrees celsius
predict what state helium is at this temperature
helium has a lower boiling point than neon so helium must be a gas at 25 degrees
radon and krypton have boiling points of -62 and -153
predict boiling point of xenon
xenon is inbetween both of these elements
(-153)+(-62) =-215
-215 / 2 = -107.5
which is approxiamately -108 degrees celsius
