Atoms and elements Flashcards
what is an element
made up of only one type of atom
what is a compound
two or more different types of elements chemicaly bonded in fixed proportions.
what is a mixture
two or more diffrent elements not chemically combined
what are sub atomic particles of an atom
proton, neutron and electron
what does the nucleus of an atom contain
proton and neuton
what is the mass of proton, neutron and electron
neutron = 1
proton = 1
electron = 0.0005 or very small
what is the charge of proton, neutron and electron
proton = +1
neutron = 0
electron = -1
location of electron
orbit shells
what does the atomic number tell you about an atom
no of protons
what does the mass number tell you about the atom
protons + neutrons
neutrons =
mass number - atomic number
why are atoms uncharged particles
they have the same number of protons and electrons that opposite charges, so they camcel each other out.
what are isotopes
atoms of the same element with the same number of protons but different number of neutrons
what is relative atomic mass
average mass of an element, taking into account the differnt masses of the isotopes, along with their relative abundances
formula for relative atomic mass
sum of ( isotope abundance * isotope mass number)/ sum of abundances of all the isotopes which is 100
what happens to alkali metals as they go down the group
they get more reactive down the group
do alkali metals have low or high melting and boiling point
low
what happens to halogens/ group 7 as they go down the group
less reactive
some features/ properties of alkali metals
soft, shiny when cut, tarnished after shiny surface exposed
why do group 1 metals act the same way
same number of electrons on outer shell
what is reactivity
greater the tendency to lose or gain electrons
what are the factors that determine how reactive elements in a groupa are
atomic radius of an element
electron shielding
why are elements in group 1 more reactive as they go down the group
they have a larger atomic radius which means the positive nucleus is further away from the negative outer electron, so there is a weaker electrostatic force of attraction, electrons are easily lost making it more reactive.
greater electron shielding, more inner electrons to shield the positive nucleus, so a weaker electrostatic attraction between the postive nucleus and the negative outer electron, so electrons are easily lost, making it more reactive.
why is fluorine more reactive than bromine
flourine has a smaller atomic radius than bromine which means there is a stronger electrostatic attraction between the positive nucleus and the negative outer electron , making it easier to gain electrons making it more reactive than bromine.
Bromine has a greater electron shielding, so ther is weaker electrostatic attraction between positive nucleus and negative outer electron, making it harder to gain electrons, making it less reactive than bromine.
describe one key fact about compounds
the properties of a compound are different from the elements they are made from.
what is a molecule
any elements chemically combined, even if they are the same element
list the physical seperation techniques
filtration. distillation. crystalisation. chromatography
filtrtaion?
seperate insoluble solid from liquid
equipment for filtration?
filter paper and funnel
Crystalisation?
seperate a soluble solid from liquid . e.g NaCL
Simple distillation?
seperate mixtures of liquids different boiling points .
Fractional distillation
seperate mixtures of liquids of similar boiling points
chromatagrophy ?
is used to separate mixtures of
soluble
substances.
list some parts of chromatography
stationary phase - paper
mobile phase - solvent
describe the plum pudding model and who came up with it
a ball of positive charge with negative electrons embedded in it
what experiment was carried out to prove the plum pudding model
alpha scattering experiment
describe the alpha scattering experiment and who did it
fired positively charged alpha particles at the gold foil. most of the particles did go straight through the gold sheet, some were deflected more than expected and some deflected backwards. Ernest rutherord and colleagues
what model of the atom came as a result of the alpha scattering experiment
nuclear model of an atom by Ernest rutherford
describe the nuclear model of an atom
atoms are mainly empty space. nucleus of the atom at the centre must have a positive charge.
nucleus of the atom is where most of the mass is concentrated in. a cloud of negative electrons surrounds nucleus
describe Bohrs nuclear model
Niels Bohr proposed that electrons orbit the nucleus at specific distances, called energy levels or shells.
who discovered neutrons
james chadwick
Give two reasons why the discovery of gallium helped Mendeleev’s
periodic table to become accepted
gallium fitted in a gap (Mendeleev had left)
.(gallium’s) properties were predicted correctly (by Mendeleev)
The plum pudding model did not have a nucleus.
Describe three other differences between the nuclear model of the atom
and the plum pudding model.
(nuclear model)
* mostly empty space
plum pudding has no empty space
nuclear model - mass is concentrated in the nucleus
plum pudding - mass is spread out through out the pudding
nuclear model - positive charge in the nucleus
plum pudding - atom is a ball of positive charge
A student suggested Mendeleev’s reason for reversing the order was to
arrange the elements in order of atomic number.
Explain why the student’s suggestion cannot be correct
.atomic number is the number of protons
.(and) protons were not discovered until later
. Give the correct reason why Mendeleev reversed the order of some pairs
of elements
so their properties matched the rest of the group
. Describe how the process of distillation produces pure water from salt solution
solution is heated
water evaporates
vapor cools in condenser
vapor condenses
water is collected in the beaker
Evidence from the alpha particle scattering experiment led to a change in the model of the atom from the plum pudding model.
Explain how
most alpha particles passed straight through the gold foil
(so) the mass of the atom is concentrated in the nucleus
some (alpha) particles were deflected / reflected
so the atom has a positively charged nucleus
. Compare the plum pudding to the nuclear model
they both have negative electrons
they both have positive charges
differences - nuclear- mass is concentrated in the nucleus while for pudding, the mass is spread out
for nuclear - the electrons are outside the nucleus while for the pudding, electrons are embedded
. Compare the physical and chemical properties of group 1 and transition metals
Physical - transition metal
. high melting point
. high density
. strong
. hard
Physical - Group 1
. soft
. low melting point
. low density
Chemical - transition metal
. form ions with different charges
. catalysts
. low reactivity
form coloured compounds
Chemical - Group 1
. very reactve
. not a catalyst
. form white colourless compounds
. only forms a +1 ion.
Tungsten is extracted from tungsten oxide
There are three methods of this extraction
Carbon - low cost, products - tungsten solid, CO2, Tungsten carbide solid
Hydrogen - high cost, products- tungsten solid and water vapour
Iron - low cost , products - tungsten solid, iron oxide solid
Evaluate three possible methods of extracting tungsten from it’s oxide.
in method 1, tungsten needs to be separated from tungsten
carbide
* in method 1, some tungsten is lost as tungsten carbide
* in method 1, the carbon dioxide produced will escape
* in method 2, the water vapour produced will escape
* in method 2, no separation of solids is needed
* in method 3, tungsten needs to be separated from iron oxide
Suggest how the student could separate the insoluble silver iodide from the
mixture at the end of the reaction.
filtration
what happens in metallic bonding?
the metal ions are held together by electrons from the outermost shell of the metal atoms. The positive ions that’s this produces are held together by strong electrostatic forces. The electrons in metals are free to move through the structure
why are metals good conductors of electricity
because the delocalized electrons carry a charge through the structure
what is an allotrope
substance containing the same type of atoms but in different arrangements eg allotropes of carbon: Graphite and diamond , graphene and fullerene, buckminsterfullerene
Explain why graphite can conduct electricity and diamond cannot
Graphite can conduct electricity because it has one delocalized electrons as graphite is covalently bonded to 3 other carbon which means it has one delocalized electron which is able to move freely throughout the structure and carry an electrical charge.
In diamond each carbon atom is covalently bonded to four other carbon atoms which leaves no delocalized electrons which means diamond has no free electrons which are able to move to carry an electric charge.
List the three giant covalent structures and explain
Diamond- . Tetrahedral arrangement. Made up of four carbon atoms. Very hard or strong because has very strong four bonds. It doesn’t conduct electricity because it has no delocalized electrons to carry a charge
It has a high melting and boiling point
Sand(Silicon oxide)- Tetrahedral arrangement. Made up of silicon and oxygen. It’s a semi conductor. It has a high melting and boiling point.
but not as strong as diamond.
Graphite- hexagonal sheets. Weak intermolecular forces, layers can slide easily. Made up of 3 carbon atoms. High melting and boiling point. Very soft. Can conduct electricity because it contains delocalized electrons.
what is covalent bonding
two or more non metals share a pair of electrons
why do most simple covalent molecules exist as a gas at room temperature
The covalent bonds within these molecules arestrong but theintermolecular forces betweenmolecules areweak and only a little bit of energy is needed to overcome theseintermolecular force between molecules.
why do ionic compounds have high melting and boiling points
when is an ionic compound able to conduct electricity
They have high melting point and boiling point due to very strong forces of electrostatic attraction between oppositely charged ions.
They have a giant lattice structure
An ionic compound is able to conduct electricity once the ions are free to move around. The ions are free to move if compounds is molten or dissolved in water
why do elements in a group react in a similar way
they have the same number of outer electron shells
What did Dobereiner notice about elements
elements with similar chemical properties often occured in threes and he called these triads
How did John Newlands arrange the elements and what did he notice about the elements and what was his famous law called
arranged based on increasing atomic weight
he noticed every eight element reacts in a similar way
law of octaves
what was wrong with John newlands method of arranging the periodic table
because he stucked with the order of increasing atomic weight, sometimes some elements were grouped with elements that had totally diffrent properties
how did Mendeleev arrange the elements
based on increasing atomic weight
what are two of the things mendeleev did to do the elements on the perodic table
he switched the order of specific elements so they fitted the pattern of other elements in the same group
he left gaps in his periodic table for elements that haven’t been discovered
did Mendeleev predict the properties of some missing elements based on the other elements in the same group?
yes
how are the elements arranged now in the modern periodic table
based on atomic number
why are noble gases so unreactive
because they have a full outer shell so they are stable
why are noble gases gases at room temperature
their boiling points are lower than room temeperature
what happens to the boiling point of noble gases as their relative atomic masses increase
boiling point increases down the group
how do metals form positive ions
they lose electrons to become stabel
what are group 1 metals called
alkali metals
do group 1 metals react very rapidly with oxygen
yes
what are group 7 elements called
halogens
what are the general observations for when alkali metals react with water
(fizzing), indicating a gas is produced.
The formation of an alkaline solution
metal+ water?
Metal + Water → Metal Hydroxide + Hydrogen
what is the reactivity trend of group 1 metals dwon the group
Group 1 metals become more reactive as you move down the group.
why do alkali metals become more reactive down the group
increasing Atomic Radius
electron Shielding
explain increasing atomic radius in terms of reactivity
As you move down Group 1, the radius of the atoms increases.
This means there’s a greater distance between the positive nucleus and the negative outer electron.
As this distance increases, there is a weaker electrostatic attraction between positive nucleus and negative outer lectron, so electrons are easily lost
Explain Electron sheilding in terms of reactivity
As you move down Group 1, elements have more electrons in internal energy levels, which increases shielding.
Increased shielding means there is a weaker electroststic attraction between the postive nucleus and the outer electron.
what type of molecules do halogens form
diatomic molecules
are halogens non metals
yes
do the melting points and boiling points of group 7 elements increase or decrease down the group
increase
what happens to the reactive of halogens down the group
become less reactive
