Atomic Structure And The Periodic Table Flashcards
What are all substances made from?
Atoms
What is an atom?
The smallest part of an element that can exist
Atoms of each element are represented by what?
A chemical symbol
How many different elements are there and where are they shown?
There are about 100 different elements. Elements are shown in the periodic table
What are compounds formed from?
They are formed from elements by chemical reactions
What do chemical reactions always involve?
Chemical reactions always involve the formation of one or more new substances and often involve a detectable energy change
What do compounds contain?
Compounds contains two or more elements chemically combined in fixed proportions
How can compounds be represented?
Compounds can be represented by formulae using the symbols of the atoms from which they were formed
How can compounds be separated?
Compounds can only be separated into elements by chemical reactions
What does the nucleus in an atom contain?
It contains protons and neutrons
Why does the nucleus in an atom have a positive charge?
It has a positive charge because of the protons
How do the electrons move around the atom?
They move around the nucleus in electron shells
Are electrons positively or negatively charged?
They are negatively charged and tiny but they cover a lot of space
Do electrons have a mass?
They have virtually no mass
Where is almost all of the mass of an atom?
In the nucleus
What does the sum of the protons and neutrons in an atom create?
Its mass number
Atoms of the same element can have different numbers of neutrons. What are these atoms called?
Isotopes of that element
Is the mass number the top number or bottom number?
The top number
Is the atomic number the top number or the bottom number?
The bottom number
What is the relative mass of a proton?
1
What is the relative mass of a neutron?
1
What is the relative mass of an electron?
Very small
What is a proton’s relative charge?
+1
What is a neutron’s relative charge?
0
What is an electron’s positive charge?
-1
In an atom what is the number of electrons is equal to?
The number of electrons is equal to the number of protons in the nucleus
Do you atoms have an overall electrical charge?
No
What does the atomic number represent?
The number of protons in an atom
Why do atoms not have an overall electrical charge?
Because they have the same number of protons as electrons
What does the mass number represent?
The mass number represents the total number of protons and neutrons in the atom
How do you work out the number of neutrons in an atom?
Subtract the atomic number from the mass number
Why does the charge cancel out in an atom?
Because the charge on the electrons is the same size as the charge on the protons but opposite so the charges cancel out
Why do ions have an overall charge?
Because in an ion the number of protons doesn’t equal the number of electrons
What is an ion?
An ion is an atom or group of atoms that have lost or gained electrons
How big is the radius of a nucleus in an atom?
1×10 to the power of -14
The radius of the nucleus is less than how much of that of the atom?
1 out of 10,000
What are isotopes?
Different forms of the same element, which have the same number of protons but different number of neutrons
Isotopes of the same except for what?
Extra neutrons
Isotopes have the same atomic number but different what?
Different mass numbers
What do mixtures consist of?
A mixture consists of two or more elements or compounds not chemically combined together
The chemical properties of each substance in the mixture are what?
Unchanged
How can mixtures be separated?
Physical processes such as filtration, crystallisation, simple distillation, fractional distillation and chromatography
When mixtures are separated by physical processes it does not involve chemical reactions so are any new substances made?
There are no new substances made
Unlike in a compound, there’s no what between the different parts of a mixture?
There is no chemical bond
What were atoms thought to be like before the discovery of the electron?
Atoms were thought to be tiny spheres that could not be divided
What did the discovery of the electron lead to?
It led to the plum pudding model of the atom
The plum pudding model suggests that the atom is a ball of positive charge with what embedded in it?
Negative electrons
The results from what experiment led to the conclusion that the mass of an atom was concentrated at the nucleus and that the nucleus was charged?
Alpha particle scattering experiment
What replaced the plum pudding model?
The nuclear model
Who adapted the nuclear model?
Niels Bohr
How did Niels Bohr adapt the nuclear model?
By suggesting that electrons orbit the nucleus at specific distances
What did later experiments lead to? What was the name of the particles?
The idea that the positive charge of any nucleus could be subdivided into a whole number of smaller particles, each particle having the same amount of positive charge. The name proton was given to these particles
The experimental work of who provided the evidence to show the existence of what within the nucleus
James Chadwick provided the evidence to show the existence of neutrons within the nucleus
At the start of which century did who describe atoms as solid spheres and said that different spheres made up the different elements?
At the start of the 19th century John Dalton
In 1897 who concluded from his experiments that atoms weren’t solid spheres?
JJ Thomson
JJ Thompson’s measurements of charge and mass showed that an atom must contain what?
Even smaller, negatively charged particles- electrons
Who conducted the famous alpha particle scattering experiment in 1909?
Ernest Rutherford and his student Ernest Marsden
How did Ernest Rutherford and Ernest Marsden conduct the alpha particle scattering experiment?
They fired positively charged alpha particles at an extremely thin sheet of gold
Why couldn’t the plum pudding model be right?
Because while most of the particles went straight through the gold sheet, some were deflected more than expected, and a small number were deflected backwards
Scientists realised that electrons in a ‘cloud’ around the nucleus of an atom would be attracted to the what causing the atom to collapse
Nucleus
Niels Bohr’s nuclear model of the atom suggested that all electrons are contained in what?
Contained in shells
What did Bohr propose about electrons?
That electrons orbit the nucleus in fixed shells and aren’t anywhere in between. Each shell is a fixed distance from the nucleus
What is relative atomic mass?
The relative atomic mass of an element is an average value that takes account of the abundance of the isotopes of the element
What is the formula to work out the relative atomic mass of an element
Relative atomic mass= sum of (isotope abundance x isotope mass number) divided by the sum of abundances of all the isotopes
In an atom what occupies the lowest available energy levels?
The electrons
How can the electronic structure of an atom be represented?
By numbers or a diagram
What do you electrons always occupy?
Shells
Which energy levels are always filled first?
The lowest energy levels are always filled first and are the ones closest to the nucleus
How many electrons are allowed in the first shell?
2
How many electrons are allowed in the second shell?
8
How many electrons are allowed in the third shell?
8
What does the atom want to do when the outer shell is not full?
React to fill it
When are atoms happy?
When they have full electron shells
Before the discovery of protons, neutrons as electrons, how did scientists attempt to classify the elements?
By arranging them in order of their atomic weight
What was wrong with the early periodic tables?
They were incomplete
Why were some elements placed in the wrong groups in early periodic tables?
Because the strict order of atomic weights had been followed
How did Mendeleev overcome some of the problems in the early periodic table?
By leaving gaps for elements that he thought had not been discovered and in some places changed the order based on atomic weights
What made it possible to explain why the order based on atomic weight was not always correct?
Knowledge of isotopes
How are elements in the periodic table arranged?
In order of atomic number and so that the elements with similar properties are in columns known as groups
Why is the table called the periodic table?
Because similar properties occur at regular intervals
What gives elements in the same group similar chemical properties?
They have the same number of electrons in their outer shell
What do elements with similar properties form?
Columns
What are vertical columns called in the periodic table?
Groups
What does the group number tell you? Except group 0
How many electrons there are in the outer shell
How do the elements react in group 1?
The elements react more vigourously as you go down the group
How do the elements in group 7 react?
Reactivity decreases as you go down the group
What are the horizontal rows called?
Periods
What does each new period represent?
Another full set of electrons
Until quite recently what with the two obvious ways to categorise elements?
Physical and chemical properties and their relative atomic mass
What are elements that react to form positive ions?
Metals
What are elements that do not form positive ions?
Non-metals
Where are metals found in the periodic table?
To the left and towards the bottom
Where are non-metals found in the periodic table?
Towards the right and the top
What do metals form when they react?
Positive ions
What don’t generally form positive ions when they react?
Non-metals
Metals to the left of the periodic table don’t have many what to remove?
Electrons
Metals towards the bottom of the periodic table have outer electrons which are a long way from the nucleus so feel what?
A weaker attraction
Why is it more difficult for non-metals to form positive ions?
Because they are either to the right of the periodic table- where they have lots of electrons to remove or towards the top- where the outer electrons are close to the nucleus so feel a strong attraction
What are the elements in group 0 called?
The noble gases
Are elements in group 0 unreactive?
Yes
Why do elements in group 0 not easily form molecules?
Because the atoms have stable arrangements of electrons
How many electrons do the noble gases have in their outer shell
The noble gases have eight electrons in their outer shell except for helium which has only two
How does the boiling point of the noble gases change
The boiling points of the noble gases increase with increasing relative atomic mass (going down the group)
What are the noble gases?
Helium, neon, argon, krypton, xenon and radon
Why does the boiling points increase as you go down group 0 (noble gases)?
It is due to an increase in the number of electrons in each atom leading to greater intermolecular forces between them which need to be overcome
As the outer shells of group 0 elements are energetically stable, they don’t need to give up or gain electrons to become more stable this means they are what?
This means they are more or less inert- which means they don’t react with much at all
What do group 0 elements exist as?
They exist as monatomic gases- single atoms not bonded to each other
At room temperature what are all the elements?
Colourless gases
Why are the noble gases non-flammable?
Because they are inert.
What are the elements in group 1 known as?
Alkali metals
Why do group 1 elements have characteristic properties?
Because of the single electron in their outer shell
In group 1, how does the reactivity of the elements change?
The reactivity of the elements increases going down the group
What do the group 1 elements look like?
They are silvery solids that have to be stored in oil as they are very reactive
What are the alkali metals?
Lithium, sodium, potassium, rubidium, caesium, francium
In which group are the elements all soft and have low densities?
Group 1- alkali metals
The first three elements in group 1 are less dense than what?
Water
How many electrons do the group 1 elements have in their outer shell?
They all have one electron in their outer shell which makes them very reactive and give them similar properties
What are the trends of alkali metals as you go down the group?
Increasing reactivity, lower melting and boiling points and higher relative atomic mass
It’s so easy for alkali metals to lose their outer electron that they only ever react to form what?
To form ionic compounds. These compounds are usually white solids that dissolve in water to form colourless solutions
What happens when group 1 metals are put in water?
They react vigourously to produce hydrogen gas and metal hydroxides—salts that dissolve in water to produce alkaline solutions
The more reactive (lower down the group) an alkali metal is the more what the reaction?
The more violent the reaction
The amount of what given out by the reaction increases down the group?
Energy-the reaction with potassium releases enough energy to ignite hydrogen
What happens when group 1 metals react with chlorine?
Group 1 metals react vigorously when heated in chlorine gas to form white metal chloride salts.
Why will the reaction with chlorine get more vigorous as you go down the group 1 elements?
Because reactivity increases
What happens when group 1 elements react with oxygen?
The group 1 elements can react with oxygen to form a metal oxide. Different types of oxide will form depending on the group 1 metal.
Why do group 1 metals tarnish in the air?
Because group 1 metals react with oxygen in the air to form a full metal oxide layer.
What are the group 7 elements known as?
The halogens
Why do group 7 elements (halogens) have similar reactions?
They all have seven electrons in their outer shell.
Are the halogens metals or non-metals?
Non-metals
The group 7 elements consist of molecules made of what?
Molecules made of pairs of atoms
How does the reactivity change as you go down the group 7 elements?
The reactivity decreases going down the group
In group 7, the further down the group an element is the higher the what?
The higher it’s relative molecular mass, melting point and boiling point
A more reactive halogen can displace a less reactive halogen from what solution?
From an aqueous solution of its salt
The halogens are non-metals with what vapours ?
Coloured vapours
What is fluorine?
A very reactive, poisonous yellow gas
What is chlorine?
A fairly reactive, poisonous dense green gas
What is bromine?
A dense, poisonous, red-brown volatile liquid
What is iodine?
A dark grey crystalline solid or purple vapour
The halogens all exist as what which are pairs of atoms?
They all exist as molecules which are pairs of atoms
Why is it harder to gain an extra electron as you go down group 7?
Because as you go down, the elements become less reactive so it’s harder to gain an extra electron because the outer shell’s further from the nucleus
Halogen atoms can share electrons via what?
Via covalent bonding with other non-metals to achieve a full outer shell
Halogens can form what sort of compounds?
Molecular compounds
What sort of bonds do halogens form with metals?
Ionic bonds
Halogens form -1 Iona called?
Halides (F-,Cl-,Br- and I-)
The compounds that halogens form have what sort of structure?
Ionic structures
More reactive halogens will do what to less reactive ones?
Displace them
