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