key concepts Flashcards
bohr model
- electrons were in a shell
- electrons exist in foxed orbits
- each shell has a fixed energy
oxidising
provides oxygen allowing other materials to burn more fiercely
environmental hazards
harmful to organisms and environment
harmful
can cause irritation reddening or blistering of the skin
toxic
can cause death
corrosive
destroys materials including living tissues
highly flammable
catches fire easily
Rutherford model
gold foil experiment
- particles went through however some were reflected
- positively charged nucleus in the centre surrounded by some negatively charged particles and a lot of empty space
- most particles went through (empty space)
JJ Thomson model
solid positively charged sphere ‘pudding’ with negatively charged particles scattered around
what does an atom contain
protons, neutrons, electron
equal number of protons and electrons
protons
heavy positively charged
neutrons
heavy
neutral
electrons
hardly any mass
negatively charged
move around the nuelus in electron sheels
tiny but sheels cover a lot of space
size of shells determed by size of aatoms
nucleus
middle of the atom contains protons and neutrons psotive charge almost whole mass is concentrated in the muckeus tiny
mass number
total number of protons and neutrons
atomic number
how many protons
isotopes
same numbers of protons, different number of neutrons
relative atomic mass
the bigger number in the periodic table
who made the first periodic table, what was wrong with it?
mendeleev
- some elements ended up in the wrong column due to isotopes
3 ideas in Dalton’s theory on an atom
- atoms can not be created, divided or destroyed
- atoms join with other atoms to make new substances
- atoms of the same element are the same
- atoms of different elements are different
structure of an atom
small central nucleus made up of protons and neutrons
electrons orbit the nucleus in shells
radius of the nucleus
1 x 10-14
1/10000 of the atomic radius
- densely concentrated
relative atomic mass of protons, neutrons and electrons
proton - 1
neutron - 1
electron - 1/2000
relative charges of protons, neutrons and electrons
proton - +1
neutron - 0
electron - -1
atoms of the same elements have the same number of …. in the nucleus and this is unique to that element
protons
how did mendeelev arrange elements
elements arranged with increasing atomic masses
similar properties in groups
left gaps for undiscovered elements
how are elements arranged in modern periodic table
in order of increasing atomic number
- similar chemical properties in groups (columns)
- the group number is the number of electrons it has in it’s outer shell
(group 7 has 7 outer shells)
elements in the same group (column) have similar ………….
chemical properties
- same number of OUTER SHELL electrons, determines how the atom reacts
elements in the same period (row)
same number of electron shells
max number of electrons allowed in each of the first 3 shells
1st - 2
2nd - 8
3rd - 8
when are atoms most stable
when they have full electron shells
what is an ionic bond
a bond between a metal and non-metal involving the transfer of electron
in terms on electrons what happens to the metal and non-metal when an ionic bond forms
the metal atom loses electrons to become a positively charged ion (cation)
the non metal atom gains electrons to become a negatively charged ion (anion)
what is an ion
an ion is an atom or group of atoms with a positive or negative charge
positively charged ion = loss or gain electrons
lost
negatively charged ion = loss or gain electrons
gain
why do elements in groups 1,2,6 and 7 readily form ions?
so they become more stable and achieve the electron structure of the noble gases (group 8)
cations
positively charged ions
anions
negatively charged ions
ions formed in group 1 and 2
1 - form +1 ions
2 - form +2 ions
ions formed in group 6 and 7
6 - 2- ions
7 - 1- ions
ionic compound that ends in -ide
compound contains 2 elements
ionic compound that ends in -ate
compound contains at least three elements, one of which is oxygen
structure of an ionic compound
- lattice structure
- regular arrangement of ions
- ions held together by strong electrostatic forces between ions and opposite charges
what is a covalent bond
a bond formed when an electron pair is shared between two atoms
a molecule forms as a result of covalent bonding
covalent bonds are strong
ionic compounds have high OR low melting points?
HIGH
strong electrostatic attraction between the positive and negative ions requires a lot of energy to overcome
simple molecular compounds have high OR LOW melting points
LOW
weak intermolecular forces = little energy to overcome
Giant covalent structures high OR low melting points
HIGH
lots of strong covalent bonds which require a lot of energy to break
how do metals conduct electricity and heat
the positive ions are fixed in a sea of delocalised electrons. These electrons are free to move and carry charge/ energy
giant covalent structures formed from carbon atoms and their structure and properties
graphite
- each carbon atom bonded to 3 other carbon atoms
- layers of hexagonal rings of carbon atoms
- weak intermolecular forces between layers
- one delocalised electrons per carbon atom
- soft, slippery
- conducts electricity
- uses: electrodes, lubricant
diamond
- all carbon atom are covalently bonded to four other carbon atoms
- no delocalised electrons
- very hard
- very high melting points
- doesn’t conduct electricity
- uses: cutting tools
what is a fullerene?
a molecule made of carbon, shaped like a closed tube or hollow ball
e.g graphene, C60 (buckminsterfullerene)
weak intermolecular forces
properties of buckminsterfullerene (C60)
- slippery
- low melting point
- spherical
- large surface area
- strong covalent bonds
properties of graphene?
- high melting point
- conducts electricity as it has delocalised electrons
what is a polymer
long chain molecules formed from many monomers
properties of metal
- high melting point
- high density
- good conductors of electricity
- malleable and ductile
- generally shiny
why are metals malleable and can conduct electricity
the atoms are arranged in uniform rows which can slide over one another
the electrons in the metal are charges that can move
properties of non-metals
- low boiling points
- poor conductors of electricity
- brittle when solid
limitations of dot and cross, 2d and 3d models, ball and stick
dot and cross - no lattice structure or ionic bonds, doesn’t shoe relative sizes of atoms or intermolecular forces
2D - only shows one layer, doesn’t show formation of ions
3D - shows spaces between the ions, doesn’t show charges
ball and stick - bonds as sticks instead of forces, doesn’t show how covalent bonds form
calculate relative former mass of a compound
add together all the relative atomic masses of the atoms in the compound
cathode
negatively charged electrode - attracts to cation
anode
positively charged electrode - attracts to anion
what are simple molecular substances
made up of molecules containing a few atoms joined by covalent bonds.
- very strong covalent bonds
- forces of attraction is weak
- mp and bp are low
examples of simple molecular substances
hydrogen - 1 electron, simple molecular bond with another hydrogen to achieve full outer shell
water - two H atoms to from 2 single covalent bonds
oxygen - needs two more electrons to complete it’s outer shell
hydrogen chloride - needs 1 more electrode
methane
- can form four covalent bonds with hydrogen atoms to fill up its outer shells
carbon dioxide - shares 2 pairs of electrons with two oxygen atoms to form two double covalent bonds
bonding models
ionic
giant covalent
metallic
simple molecular (covalent)
ionic bonding model
found: in most compounds containing metal and non-metal atoms
bonding: ionic bonds formed by the loss and gain of electrons to produce oppositely charged ions that attract on another
structure: billions of ions held together in a lattice structure
properties: high melting point, many are soluble in water, conduct electricity when liquid or in solution (not in solid)
simple molecular bonding models
found: in most non-metal elements and compounds
bonding; covalent bonds formed when atoms share pairs of electrons
structure: small, distinct groups of atoms
properties: low melting points, few are soluble in water
giant covalent boning models
found: in a few non-metal elements and compounds
bonding: covalent bonds formed when atoms share pairs of electrons
structure: billions of atoms held together in a lattice structure
properties: high melting point, insoluble in water, most do not conduct electricity (except carbon in graphite)
metallic bonding model
found: in all metals
bonding: metallic bonds are the electrostatic attraction between positive metal ions and negative delocalised electrons.
structure: billions of ions held together in a giant lattice structure of positive ions in a ‘sea’ of delocalised electrons
properties: high melting point, insoluble in water, , conduct electricity when solid or liquid
