topic C1-Atomic Structure and the Periodic Table Flashcards
What is an atom?
An atom is the smallest part of an element
What is an element?
made up of only one type of atom
Elements may combine through chemical reactions to form new products; what are these new substances called?
compounds
What is a compound?
contains 2 or more different elements chemically combined in a fixed proportion
compounds can be separated by
chemical separation
What is a mixture?
A mixture consists of two or more elements or compounds not chemically combined together
mixtures are separated by
physical separations
What are the methods through
which mixtures can be separated
(there are five)? Do these involve
chemical reactions?
Filtration, crystallisation, simple distillation, fractional distillation chromatography they do not involve chemical reactions
Describe and explain filtration
separates insoluble solids from liquids
- filter paper placed in a funnel over a conical flask
- pour mixture through the funnel
- insoluble particles are left on the filter paper
Describe and explain crystallisation/evaporation.
used to separate a soluble solid from solvent by evaporation
-pour the solution into a evaporating dish
-gently heat the solution until all the solvent evaporates
-the solution
(crystallisation)
Crystallisation is similar, but we only remove some of the solvent by evaporation to
form a saturated solution Then,
we cool down the solution. As we do it, the solid starts to crystallise,
Required Practical 1 method-Making Salts
- using a measuring cylinder measure (20 cm of sulfuric acid ) of acid into a beaker
- add powdered metal into the acid and stir with a glass rod
- continue adding the powder until it is in excess so no more reacting occurs eg fizzing
- set up Filter using filter paper and funnel the solution to remove the excess solid (copper oxide.)
- Pour the solution into the evaporating dish.
- Evaporate the solution using a water bath until crystals start to form.
- Leave the evaporating basin in a cool place for at least 24 hours.
- Gently pat the crystals dry between two pieces of filter paper.
why do you need to put excess powder
so that no more reaction occurs
Describe and explain the simple distillation
Simple distillation is used to separate liquid from a solution – the liquid boils off and condenses in the condenser. The thermometer will read the
boiling point of the pure liquid.
the problem with simple distillation
if the solution of liquid have the same boiling point than the liquids cannot separate
explain
fractional distillation
Fractional distillation is a technique for separation of a mixture of liquids.
It works when liquids have different boiling points.
liquid with the lowest boiling point evaporates first
liquid with the highest boiling point condense at the bottom
simple distillation - method
- start off by heating the solution eg using a Bunsen burner
- the part of the solution with the lowest boiling point evaporates first
- the liquid turns into vapour and passes into the condenser
- the vapour then cools and condenses turning back into a liquid
- crystal solids are left behind in the flask and the liquid is collected in the beaker
fractional distillation - method
The apparatus is similar to the one of simple distillation apparatus, with the
additional fractionating column placed on top of the heated flask.
The fractionating column contains glass beads. It helps to separate the compounds. The column is hot at
the bottom and cold at the top. The liquids will condense at different heights of the column.
Describe and explain chromatography
Chromatography is used to separate a mixture of substances dissolved in a solvent.
paper chromatography, we place a piece of paper with a spot containing a mixture
in a beaker with some solvent. The bottom of the paper has to be in contact with
the solvent. The solvent level will slowly start to rise, thus separating the spot (mixture) into few spots (components).
john Dalton
thoughts that atoms are tiny solid spheres that cannot be divided
jj Thomson
discovered electrons which led him to the plum pudding model
Describe the plum-pudding model
The atom is a ball of positive charge with negative electron embedded in it.
Ernest Ruthford
the alpha scattering particles experiment
which led him to the conclusion that mass of an atom was concentrated at the centre (nucleus) and that the nucleus is a positively charged
alpha scattering particle
- a beam of alpha particles was fired at a thin gold foil
- most particles went straight through the gold foil
- some alpha particle was deflected and some repelled
what did the alpha scattering experiment tell us
most alpha particles went straight through therefore atoms are mainly empty space
some of the particles were deflected therefore the centre of an atom must have a positive charge
- empty space
- positive nucleus
- surrounded by electrons
Neil Bohr
suggested the nuclear model
- suggested that electrons orbit the nucleus at a certain distance
Describe the Bohr/nuclear model and how it came about
The nuclear model suggests that electrons orbit the nucleus at specific
distances (shells) – it came about from the alpha scattering experiments
later on the experiment
led to the discovery of protons - positive particle in the nucleus
James Chadwick
included that the nucleus contains neutrons
overview of the plum pudding model
- mainly empty space
- positive nucleus
- surrounded by negative electrons
overview of the nuclear model
electrons - orbit the nucleus at a specific distance - called shells or energy levels
the positive charge in the nuclear is due to tiny positive particles called protons
nucleus contains neutral particles called neutrons
State the relative charges
of the proton, neutron and electron
proton - +1
neutron- 0
electron - -1
State the relative mass
of the proton, neutron and electron
proton - 1
neutron - 1
electron -very small
What is the radius of an atom?
0.1 nm
What is the radius of a nucleus and
what is it compared to that of the
atom?
1 x 10-14 m and 1/10000
What name is given to the number of protons in
the nucleus?
Atomic number
Where is the majority of mass of an atom?
The nucleus
What is the mass number?
The total number of protons and neutrons
How does one calculate the
number of neutrons using mass
number and atomic number?
Subtract the atomic number from the mass number
What is an isotope? Do isotopes of a certain element have the same chemical properties?
Atoms of the same element (same proton number) that have a different number of neutrons. They have the same chemical properties as they have the same
electronic structure
What is the relative atomic mass?
The average mass value which takes the mass and abundance of isotopes
of an element into account, on a scale where the mass of 12C is 12.
What are ions?
Ions are charged particles. They are formed when atoms lose electrons
(positive ions) or gain (negative ions) electrons.
properties of metals
Boiling/meting point -High Conductivity- good conductor of heat and electricity Appearance -Shiny Malleability - yes Density - High Oxides-Basic
properties of non-metals
Boiling/meting point-low Conductivity-cannot conduct Appearance-dull Malleability-brittle Density-low Oxides-acidic
What is formed when a metal reacts with a
non-metal?
An ionic compound (made of positive and negative ions).
What is formed when a non-metal reacts with a non-metal?
A molecular compound containing covalently bonded atoms.
Atoms share electrons, as opposed to transferring electrons between each other
the periodic table
the elements are arranged in order of increasing atomic number
The columns of the periodic table are called?
Groups
group number
number of electrons in the outer shell
The rows of the periodic table are called…?
Periods
periods
number of shells
Are elements in the same group similar or
different?
They may have similar chemical properties, as they have the same
number of outer shell electrons.
Early periodic tables
john Newlands
-arranged the elements in order of atomic mass
-every 8th elements reacts in the same way
-the period was
incomplete and elements were
placed in inappropriate
law of octaves
every 8th element reacts the same way and have similar properties
Early periodic tables were incomplete and
elements were placed in inappropriate groups if what was to be followed?
The strict order of atomic mass
Knowledge of what made it possible to explain
why the order based on atomic weights was not
always correct?
Isotopes
modern periodic table
Dmitri Mendeleev
- put the elements mainly in order of atomic mass but did switch /changed the order based on properties/weights
- and left gaps for elements that have not been discovered yet
Mendeleev overcame some problems with the table by doing what? He also changed the order of some elements based on what?
Leaving gaps and changing the order based on atomic weights
Elements that react to form positive ions are…?
Metals
Elements that do not form positive ions are…?
Non-metals
Elements in Group 1 are known as…?
The alkali metals
State three characteristics of
the Alkali Metals
-All have one electron in their outer shell
-have low density
-are stored under oil (to prevent reactions with oxygen or water)
are soft (can be cut
with knife)
-very reactive
How do Group 1 elements react with
non-metals? Why are these reactions similar for the different Group 1 elements?
They form ionic compounds which are soluble white solids which form
colourless solutions – they all have one electron in their outer shell.
reactivity in group one
the reactivity of the element increases as you go down the group . this is because the attraction between the nucleus and electrons decease
How do Group 1 elements react with water?
They release hydrogen and form hydroxides which dissolve to form
alkaline solutions; react vigorously with water fizzing and moving around
on the surface of the water.
lithium reacts with water
reaction with water - fizzes steadily floats/moves around
lithium reacts with chlorine
white power
lithium reacts with oxygen
produces white solid
burns with red flames
sodium reacts with water
fizzes furiously melts into a ball disappears quicker
sodium reacts with chlorine
clouds of white burns with yellow flame
sodium reacts with oxygen
strong orange flame white solid
potassium reacts with water
ignite with sparks
lilac flame , disappears quickly
potassium reacts with chlorine
even more vigorous
potassium reacts with oxygen
lilac flames
group 7 also known as
halogens
State five characteristics of Group 7
- 7 electrons in outer shell
- Coloured vapours
- Diatomic molecules
- Form ionic salts with metals
- Form molecular compounds with non-metals
fluorine
yellow gas and very reactive
chlorine
green gas and fairly reactive and poisonous
bromine
red-brown gas dense and poisonous
iodine
grey as solid
purple as vapour
State three changes that occur in Group 7 as one moves down the group
- Higher relative molecular mass
- Higher melting and boiling point
- Less reactive – less easily gain electrons
A more reactive halogen displaces a less reactive one from an aqueous solution of its salt; explain the trend in reactivity of halogens in these reactions
Reactivity decreases down the group. As we go down the group, the atoms
get larger, so an incoming electron will be less tightly held by the attractive forces
from the nucleus. That’s why Cl2
displaces Br–
and I–
Compare group 1 metals with transition metals
Group 1 metals and transition metals are heat and electricity conductors.
They are shiny when polished and form ionic compounds with non metals.
Transition metals have higher densities and higher melting points than Group
1 metals. They are less reactive and harder than Group 1 metals.
State three common characteristics of transition metals
- Ions with different charges
- Coloured compounds
- Catalytic properties
Describe the properties of noble gases. Discuss
the trends in properties down the group.
Non-metals, gases, low boiling points, unreactive (full outer shell; they don’t easily accept or lose electrons). The boiling point increases down the group, as the atoms get heavier.
