✅ 1. Atomic structure & the Periodic Table Flashcards
What are all substances made up of?
All substances are made up of atoms
Describe what an atom is
An atom is the smallest part of an element that can exist
How can atoms be represented?
Atoms can be represented by chemical symbols
What is an element?
An element is one type of atom
Around how many different elements are there?
There are around 100 different elements
What is a compound?
A compound isa group of 2 or more elements that are chemically combined together in fixed proportions
e.g. for carbon dioxide, there are 2 oxygen atoms for each carbon atom
How are compounds formed and separated?
Compounds are formed and seperated by chemical reactions
How do we separate compounds back into their elements?
We can seperate compounds back into their elements using chemical reactions
How can compounds be represented?
Compounds can be represented by formulae using the symbols of the atoms from which they were formed
What do chemical reactions always involve?
- Energy changes
- Production of one or more new substances
How can chemical reactions be represented?
Chemical reactions can be represented by word equations or equations using symbols and formulae
Describe the relationship between the properties of compounds and the elements they are made from?
Compounds have totally different properties from the elements that they’re made from
What does a mixture consist of?
A mixture consists of two or more elements or compounds not chemically combined together
Give three differences between a mixture and a compound
- A compound consists of two or more elements that are chemically combined together, whereas a mixture consists of two or more elements and compounds that are not chemically combined together
- Mixtures can be separated by physical techniques rather than chemical reactions
- In a mixture, the chemical properties of each substance stays the same
What is a molecule?
A molecule is any element that is chemically combined (even the same element)
When do we use filteration?
Filteration is used to seperate an insoluble solid from a liquid
When do we use crystalisation?
Crystalisation is used to seperate a soluble solid from a solution
When do we use simple distillation?
Simple Distillation can be used to seperate a solvent from a solution
When do we use chromatography?
Chromatography can be used to seperate a mixture of substances based on their solubility
What may lead to a scientific model being changed or replaced?
New expermental evidence that doesn’t agree with the existing theory
What were atoms thought to be before the discovery of the electron?
John Dalton Model
Atoms were initially thought to be tiny spheres that could not be divided
John Dalton Model
What happened in 1897?
In 1897, J.J Thomson discovered the electron which led to his proposal of the plum pudding model in 1904
Which scientist discovered electrons?
JJ Thomson discovered the electron
What model did Thomson create after the discovery of the electron?
The discovery of the electron led to the creation of the plum pudding model
What did the plum pudding model suggest?
The plum pudding model suggested the the atom was a ball of positive charge with negative electrons embedded in it
How was the plum pudding model disproved?
The plum pudding model was disproved by the results from Rutherford’s alpha particle scattering experiment
Describe what happened in the alpha particle scattering experiment?
- A beam of positively charged alpha particles were aimed at a thin gold foil
- Most of the alpha particles passed straight through the gold foil without changing direction
- Some were slightly changed direction but passed through the foil
- Very few particles bounced back off the gold foil
What were the results of the alpha particle scattering experiment?
Rutherford concluded that:
- Most of the atom consisted of empty space as most alpha particles went straight through the gold foil
- The nucleus must have a positive charge as some alpha particles were deflected
- The mass of the atom must be concentrated at the centre as few numbers of alpha particles rebounded straight back
This became known as Rutherford’s nuclear model
What did Rutherford do after the alpha particle scattering experiment?
Rutherford created the nuclear model after the alpha particle scattering experiment, which replaced the Plum Pudding Model
What did Neil Bohr do?
Niel Bohr adapted the nuclear model by suggesting that electrons orbit the nucleus in shells that are at specific distances
Why was Bohr’s model accepted?
The theoretical calculations of Bohr agreed with experimental observations.
What did James Chadwick do?
20 years after the nucleus became an accepted scientific
idea and the nuclear model, James Chadwick demonstrated the existence of neutrons
What are the 3 subatomic particles
- Protons
- Neutrons
- Electrons
Describe the structure of an atom?
The atom has a small, central nucleus made up of neutrons and protons, around which there are electrons
What is the charge of atoms?
Atoms have no overall charge
Why do atoms have no overall charge?
There is no overall charge as they have the same number of protons as electrons, so the charges cancel each other out
What does the atomic number represent?
The atomic number represents the number of protons
(The no. of protons defines an element)
What do all atoms of a particular element have in common?
All atoms of a particular element have the same number of protons
(The no. of protons defines an element)
What is the atomic mass?
The total number of protons and neutrons
What is the radius of an atom?
The radius of an atom is about 0.1 nm (1 x 10-10 m)
Compare the radius of the nucleus to the radius of the atom?
The radius of the nucleus is around 10 000 times smaller than the radius of the atom (1 x 10-14)
What are isotopes?
Isotopes are atoms of the same element that have the same number of protons, but different number of neutrons, hence a different mass number
What do all isotopes have in common?
Isotopes have the same number of protons (and electrons?)
Why do isotopes of an element have identical chemical properties?
Isotopes of an element have identical chemical properties because they have the same number of electrons
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
How do we find out the relative atomic mass?
How do electrons orbit the atoms?
Electrons orbit the atoms in energy levels / shells
What is the lowest energy level of atoms?
The lowest energy level of atoms is shown by the shell closest to the nucleus
Describe the behaviour of electrons and energy levels
The electrons in an atom tend to occupy the lowest available energy levels
As the distance from the nucleus increases, what happens to the energy levels?
As the distance from the nucleus increases, the energy of each energy level increases
What is another word for energy levels?
Shells
What is the maximum number of electrons the first four shells can hold?
- 1st energy level / shell - 2 electrons
- 2nd energy level / shell - 8 electrons
- 3rd energy level / shell - 8 electrons
- 4th energy level / shell - 18 electrons
What are columns in the periodic table known as?
The columns in the periodic table are known as groups
What are the rows in the periodic table known as?
The rows in the periodic table are known as periods
How are the elements of the periodic table arranged?
The elements of the periodic table are arranged in order of increasing atomic number
How do we determine the number of electrons on the outer shell of an element?
By looking at their group number
Why do elements in a group have similar chemical properties?
Elements in the same group have similar chemical properties because they have the same number of electrons on their outer shell, so they will all react in similar ways
How did early scientists attempt to sort elements in the periodic table?
Early scientists tried to order the elements by arranging them in order of their increasing atomic weights
John Newland
- John Newland was the first early scientist to devise a periodic table
- He arranged the elements in order of increasing atomic weight
- However, the tables were incomplete and and some elements were placed in innappropriate groups if the strict order of atomic weights was followed
What were two problems with the early periodic table?
- The tables were incomplete
- Some elements were placed in inappropriate groups if the strict order of atomic weights was followed
Explain what Dmitri Mendeleev did
- Dmitri Mendeleev arranged the elements in the order of increasing atomic weight as other scientists had done
- However unlike other scientists, he would not arrange it strictly in the order of atomic mass and would sometimes switch the order of specific elements so that they fitted the properties of other elements in the same group
- He also left gaps for elements that he thought had not been discovered yet
Explain two differences Dmitri Mendeleev made to his periodic table
- He did not arrange elements strictly in the order of atomic mass and would sometimes switch the order of specific elements so that they fitted the properties of other elements in the same group
- He also left gaps for elements that he thought had not been discovered yet
What happened to the elements predicted by Mendeleev?
Elements with properties predicted by Mendeleev were discovered and filled the gaps in his periodic table
How are modern day periodic tables arranged?
Modern day periodic tables are arranged in order of atomic number (the no. of protons)
Give two reasons why it was difficult for Mendeleev to arrange the periodic table completely right?
- Protons had not been discovered then, so he would not be able to arrange elements according to their atomic number
- Mendeleev did not know about isotopes, which is why the order based on atomic weights was not always correct
Why did scientists accept that Mendeleev’s table was correct?
- Scientists accepted that Mendeleev’s table was correct because he predicted the properties of undiscovered elements based on the other elements in the same group
- Several years later these elements were discovered
The majority of elements are… ?
The majority of elements are metals
How do we identify which elements are metals?
Elements that react to form positive ions are metals
How do we identify which elements are non-metals?
Elements that do not react to form positive ions are non-metals
Where are metals found in the periodic table?
Metals are found to the left and towards the bottom of the periodic table
Where are non-metals found in the periodic table?
Non-metals are found towards the right and top of the periodic table
Why do metals react?
Metals react to lose electrons to form a full outer shell
Why is the metal Lithium in group 1?
Because it has one electron on its outer shell
Explain the the physical properties of metals
- Metals have high metling and boiling points
- So they are all solids at room temperature (except for mercury)
- They are good conductors of electricity and thermal energy
- They appear shiny
Explain the the physical properties of non-metals
- Non-metals have lower melting and boiling points
- They are found as gases
- They generally do not conduct electricity or thermal energy
- They appear dull
Hydrogen is a non-metal. It can form H+ and H- ions.
Explain why this is unusual
Non-metals are elements that do not form positive ions, but hydrogen can form positive ions just like metals
The metal mercury is liquid at room temperature.
Explain why this is unusual.
Metals are usually solids at room temperature that have high melting and boiling points
What are group 0 elements also known as?
Group 0 elements are also known as noble gases
Describe the chemical properties of group 0 elements?
- They are unreactive elements
- They have a full outer shell of electrons
Describe the electron structure of the noble gases?
The noble gases have a full outer shell of 8 electrons, except for helium which has two
Why are noble gases unreactive?
Because their atoms have stable arrangements of electrons (a full outer shell)
Why are noble gases monatomic (exist in single atoms)?
Because the noble gases have a stable electronic structure
Describe the physical properties of group 0 elements
Noble gases have low boiling points
Their boiling points increase as you go down the group (as their relative atomic masses increase)
What are Group 1 metals known as?
Group 1 metals are known as Alkali metals
Why do Alkali metals have their characteristic properties?
Alkali metals have their characteristic properties because of the single electron in their outer shell
Describe the reactivity of alkali metals as you go down the group
As you go down the group, the reacitivty of the elements in Group 1 increase
Why does the reactivity of Group 1 elements increase as you go down the group?
The reactivity of Group 1 elements increase as you go down the group because:
1. Atoms get larger due to the increase in relative atomic mass
2. So the distance between the outer electron and nucleus increases as electrons gain more shells
1. The attraction between the outer electron and nucleus decreases and gets weaker
1. So the outer electron is lost more easily
Why are alkali metals generally very reactive?
Alkali metals are very reactive as they only need to lose one electron to have a stable electronic structure
What happens to the melting and boiling points as you go down the Alkali group?
The melting and boiling points decrease as you go down the group
Do reactive elements react slowly or rapidly?
Rapidly (and vigorously)
Describe the reaction of Lithium with Oxygen
- Lithium reacts with a red flame
- It is the least reactive alkali metal compared to sodium and potassium
Why may Sodium be more reactive than Lithium?
Because its outer electron is further away from the nucleus, so it is less attracted to the nucleus and so it is easier to lose the electron
Describe the reaction of Sodium with Oxygen
- Sodium reacts with Oxygen to produce an orange flame
- It is the least reactive alkali metal compared to potassium, but more reactive than Lithium
Of the first three Alkali metals (Lithium, Sodium Potassium), which metal is the most reactive
Potassium
Describe the reaction of Potassium with Oxygen
Potassium reacts with Oxygen to produce a lilac flame
What do alkali metals react with water to produce?
Alkali metals react with water to produce metal hydroxides and hydrogen
Describe the reactions of the first three alkali metals with water
Alkali metals react with water to produce metal hydroxides and hydrogen
* Lithium floats on the water and fizzes steadily, producing bubbles of hydrogen gas
* Sodium floats on the water and melts into a silvery ball, before fizzing rapidly and producing an orange flame
* Potassium floats on the surface of the water, and then reacts vigorously and then burns with a lilac flame
What do all alkali metals do when reacting with water?
All alkali metals flot on the surface of the water before reacting
Describe the reactions of alklai metals with chlorine
- Alkali metals react with chlorine to form Metal Chlorides, which are white solids
- The white solids dissolve readily in water to form colourless solutions
- Lithium burns with a red flame
- Sodium burns with an orange flame
- Potassium burns with a lilac flame
- Potassium reacts the most vigorously with chlorine
What are elements in group 7 known as?
Elements in group 7 are known as halogens
Why does every element of the halogens have similar chemical reactions?
Because they all have 7 electrons on their outer shell
Give 5 characteristics of Halogens?
- They are non-metals
- They have 7 electrons on their outer shell
- They exist as diatomic molecules, bonded through covalent bonds
- They react with metals to form ionic compounds / salts
- They react with non-metals to form covalent compounds
Describe the physical properties of group 7 elements
- They have low melting and boiling point
- The melting points and boiling points increase as you go down the group
- The relative molecular mass increases as you go down the group
Explain the trend in reactivity as you go down group 7
As you go down group 7, the reactivity of the elements decreases
This is because:
- Atoms get larger due to the increase in relative atomic mass
- So the distance between the outer electrons and nucleus increases as electrons gain more shells
- The attraction between the outer electrons and nucleus decreases and gets weaker
- So it is harder for the atom to gain attract electrons from other atoms
Describe the reaction between Chlorine & Potassium Bromide
& explain why
Chlorine + Potassium Bromide → Potassium Chloride + Bromine
- A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt.
Compare group 1 metals with transition metals
Alkali metals:
- Are very soft (can easily be cut with a knife)
- Relatively lower melting points
- They have low densities
- They react very rapidly with oxygen, chlorine and water
- They only form ions with 1+ positive charge
Transition metals:
- Are hard and strong
- Have relatively higher melting points (except for mercury, which is liquid at room temperature)
- Have high densities
- They are much less reactive as they do not react easily with oxygen, chlorine or water
- They can form ions with different charges (Fe2+, Fe4+, Ni2+, Ni2+)
Give 3 chemical characteristics of transition metals
Many transition elements have ions with different charges, form coloured compounds, and are useful as catalysts
Describe what the roman numerals outside transition elements are for?
e.g. Iron(II), Iron(III)
The roman numerals outside the brackets distinguish ions of the same element that have a different number of electrons on the outer shell
e.g. Fe2+ is the Iron(II) ion
Fe3+ is the Iron(III) ion
