chemistry Flashcards
chemistry exam
Which particle determines what element an atom is?
- PROTONS
Which sub-atomic particle does NOT have a charge?
-NEUTRONS
If an atom has 6 protons and 5 electrons, what charge will it have overall?
+1
Which particles within an atom have a relative mass of 1?
PROTONS AND NEUTRONS
Electrons orbit the nucleus in energy …
Electrons orbit the nucleus in energy shells.
What do we call an atom that has a positive or negative charge?
AN ION
An atom has 13 protons and 14 neutrons. What is its mass number?
27
What are isotopes?
Atoms of the same element with different numbers of neutrons
Four atoms have the numbers of protons and neutrons given below. Which two atoms are isotopes of the same element?
Atom W: 11 protons and 10 neutrons
Atom X: 10 protons and 10 neutrons
Atom Y: 9 protons and 9 neutrons
Atom Z: 10 protons and 9 neutrons
X AND Z
Lithium naturally exists as two isotopes: lithium-6, with an abundance of 7.6%, and lithium-7, with an abundance of 92.4%.
6.92
When Democritus first conceived of atomic theory, around 500 BC, how did he describe atoms?
- The smallest possible unit of matter
- Separated from each other by empty space
- Small spheres
In 1897 J. J. Thomson theorised that an atom consisted of a ball of positive charge, with negative electrons mixed throughout it. What do we call this model?
plum pudding model
In the 1800’s, John Dalton described atoms as …..
, and suggested that different types of spheres make up the….
.
- solid sphers
- different elelemnts
In Rutherford’s experiments, alpha particles were fired at a thin sheet of gold foil.
Most particles passed through, but some were deflected off course.
This caused him to hypothesise that there was a dense region of positive charge at the centre of the atom that repelled the alpha particles.
As a result he developed the nuclear model of the atom, in which there was a central positive nucleus, surround by negative electrons.
An atom of oxygen has 6 electrons in the outer shell. In a reaction, it gains 2 electrons.
What is the charge of the oxide ion created?
2-
definition of isotopes?
isotopes are the same element that have the same number of protons but a different number of neutrons.
smallest element in the periodic table?
hydrogen
what do different isotopes have?
- different masses
how do isotopes react even though they have different number of neutrons?
- they react the same way
how to calculate the relative mass of two isotopes?
sum of abundance of all isotopes
what does it mean when an atom is not stable?
doesnt have a full other shell
what do not stable atoms do?
react with other atoms to become more stable
,eaning of stable in electrons
outermost shell is full
define a group in period table with full outer shell
noble gases have a full outer shell
in an exam what do they mean by electron structure?
they mean draw the electron, if it gained an electron put brackets an mines the amount of electrons you gained if you loose the electrons do the same thing with brackets but put a plus whatever the number of electrons you added
what is the first group in the periodic table?
alkali metals
what is group 7 in the periodic table?
halogens
what is the tomic number?
number of protons and neutrons
in the periodic tbale what does a row present?
a period
in the periodic tbake what does a column present?
a group
what do metals form?
when metals react what do they form?
positive ions
when non metals react what do they form?
negative ions or dont form ions
as you go down in the periodic table the metals tend to be more reactive, why is that?
because the elements far down the table have lots of shells, so outermost shell is far from the nucleus it would be harder for the nucleus to keep the electrons and it woudl be easier for the elctrons to loose and make the atom positive
more reactive as they are more likely to loose electrons during a reaction.
what hold the negative electrons in place that doesnt make the collapse?
the positive nuclus in the middle
physical properties of metals: (6)
- mallable- can bent without snapping
- metallic bonding- occurs only in metals and very strong
- good conductors of heat and electricity- thats why we use them in electric wires
- high melting and boiling point
- shiny
- sonorous
physical properties of non metals: (5)
- dull in colour
- brittle easily break
-low melting and boiling point - lower density so weight less for different volume
- poor conductors of electricity
where are transition metals found?
centre if periodic table in the middle of group 2-3
transition metals
normal metals with extra properties:
- can form more than once ion that have their own section
- coloured: transition metal ions are colored
- good catalysts
what is a catalyst?
substance that speeds up a chemical reaction without being used up
Alkali metals react with water. Which two products are formed?
Alkali metal + water ➔ metal hydroxide + hydrogen
Explain why the reactivity of group 1 metals increases as you go down the group.
The reactivity of group 1 elements increases as you go down the group because the atoms become larger, which means that the outer electron becomes further from the nucleus.
This in turn means that the electrostatic attraction between the positive nucleus and the outer negative electron decreases in strength.
As a result the outer electron will be lost more easily, and so the element will be more reactive.
When sodium reacts with chlorine it forms an ionic salt called ….
sodium chloride.
Some of the compounds formed when alkali metals react with oxygen
Lithium reacts with oxygen to form lithium oxide, Li2O.
Sodium reacts with oxygen to form sodium oxide, Na2O or sodium peroxide, Na2O2.
Potassium reacts with oxygen to form potassium peroxide, K2O2, or potassium superoxide, KO2.
properties of alkali metals:
- soft
- low melting point
- low density
describe reactivity of alkali metals
as you go down the alkali metals become more reactive
with what elements do alkali metals react a lot with?
water, oxygen, group 7 elements
melting point of alkali metals as you go down
the melting point decreases
Why are alkali metals so reactive ? why the further down u go the metals get more reactive?
all alkali metals have one elecron intheir outermost shell, to be stable they need to loose on electron then become a positive ion as you go down the alkali metals become more reactive as they radius gets bugger meaning there ismore distact between positive nucleus that keeps electron in place and the electrons, weakening the attractive force making it easy to lose the electron increasing atom reactivity
what do alkali metals + water form?
Alkali metals + water —-> metal hydroxide + hydrogen gas
what do alkali metals + chlorine form?
white metal chlorine salt
what do alkali metals + oxygen form?
metal oxide
what do metals form?
positive ions
what do non metals form?
- dont form ions or negatuve ions
in alkali metals asyu go down…
reactivity increases
are haongens dangerous?
YES
what is florine?
poisonous yellow gas and very reactive
what is chlorine?
less reactive, and it is a poisonous green gas
what is bronie?
a brown posonous liquid,
what is iodine?
dark gray solid, can form poisonous purple vapours or alos an anitisepctic
halogen exist as pairs of atoms that we call…
diatomic molecules
how do halogen form diatomic molecules?
by sharing pair of electrons, also known as convalent bonding
what does diatomic molecules mean?
2 pairs of atoms
in alkali metals as yo go down what happens to the melting and boiling point?
in alkali metals as you go down the melting point decreases
in halogens as yo go down what happens to the melting and boiling point?
as you go down the periodic table, in halogens the meltig and boiling point increases and reactivity decreases
what do we a call halogen that gains an electron to form a one minu sion?
halide, we chnage the nd with ide and would be ions
what are displacement recations?
a more reactive halogen displacing a les reactive one
what are noble gases?
colorless gases
whta happens to the boiling point of noble gases as we go down the periodic table?
increases, like halogens
why are noble gases inert?
they have a full outer shell
important things to know about noble gases?
- dont react with anything
- singel atoms
- non flammable cant be set on fire
- boiling poit increases as you go down thw group
what color is bromine water?
orange
what color is iodine?
iodine water is brown
what color is chlorine?
colorelss
in group seven what is the charge?
-1
We measure the acidity or alkalinity of a solution using the
scale.
ph
The pH scale ranges from:
0-14
two ways by which the pH of a solution can be measured.
pH probe
Chemical indicator
What term can be used to describe solutions with a pH of 7?
neutral
what is an universal indicator?
ndicator is made up of a several different indicator solutions. This means that it undergoes a smooth colour change over a wide range of pH values.
The pH of a solution can be measured using a type of chemical dye that changes colour, depending on the pH of the substance it’s mixed with.
This chemical dye is usually referred to as:
indicator solution
A pH probe electronically measures the pH of a solution. two reasons why using a probe may be more reliable than using an indicator.
A probe produces a more accurate result
Determining the colour of an indicator is subjective
Select the ion responsible for making an alkaline pH when dissolved in solution
OH-
definition of an acid?
any substnace that forms a solution with a ph scale less than 7
Which formulae represents nitric acid?
HNO3
what does CO3 mean?
carbonate
methods we can use to measure ph scale?
- colorimetric methods using indicator solutions or papers
- universal indicator
- ph probe with ph metre-more accurate
what does a universal indicator show us?
can show us how strongly acidic or alkaline a solution is, not just that the solution is acidic or alkaline
what do alkali substances form?
hydroxide ions- OH¯
what do acidic substances form?
RELEASE HYDROGEN IONS- H+
whta is a neutralisation reaction?
solution that is when an acidic recats with a base, and it forms salt +water
what does it mean conservation of mass?
no atoms are created or destroyed, however only the bonds change
what happens to the mass throught the reaction of conservationals mass?
the mass should stay the same but there is an exception: when reaction involves gas, mass might seem to change, wont be measured be scales
conservation of mass principle
mass is always conserved in a chemical reaction
in conservation of mass why would the mass appear to change? and how can we solve this?
- if mass increases: because one of Reactants is a gas
- if mass decreases: one of your products is a gas
how can we avoid this?
- do the experiment in a sealed container
Which particles within an atom have a relative mass of 1?
proton and neutron
What is a chemical change?
A rearrangement of the atoms in the reactants, to form the products
In a chemical reaction, is there any change in the overall mass of the substances?
NO
A chemical reaction is carried out in a beaker on a balance.
Why may the balance reading for the products be less than the reading for the reactants?
- One of the products was a gas and floated off
- Some of the reactants may have been spilled
ph scale?
meausre of how acididc or alkali a substance is from a scale from 0 to 14
universal indicator
indicator that shows how acidic or how alkali a subtance is, going from dark red to yellow, green, blue and purple
what cane we use to test the ph of a subctance
an indicator, a chemical dye that chnages color based on how acidic or alklai a substance is
what is the difference between wide range indicators and universal indicator
a universal indicator is more precisive when it comes to the color system.
- color
- range
- precision is better with the universal indicator
another way after indicators to measure ph of a substance?
ph tube connected to a ph meter and dipping the ph tube into the substance and the ph meter is going to tell us what substance it is
difference betwwen probe and indicator
probe is more precisive because doesnt involve gessing shades,
what do acids release that makes them acidic
hydrogen ions in water
alklais soluble in water yes or no?
yes
what do bases produce?
hydroxide ions
what do acids and alkali produce?
neutralisation reaction that will always produce salt plus water
what is an alkali
a base that dissolves in water to form a ph grater than seven
