Topic 1: Key Concepts in Chemistry Flashcards
What does a chemical formula show?
The proportion of atoms of each element in a compound
What does a chemical equation show?
The overall change in a reaction
What does the state symbol (s) represent?
Solid
What does the state symbol (l) represent?
Liquid
What does the state symbol (g) represent?
Gas
What does the state symbol (aq) represent?
Aqueous
What does aqueous mean?
Dissolved in water
What is the chemical formula of ammonia?
NH₃
What is the chemical formula of ammonium?
NH₄⁺
What is the chemical formula of hydroxide?
OH¯
What is the chemical formula of nitrate?
NO₃ ¯
What is the chemical formula for carbonate?
CO₃ ²¯
What is the chemical formula for sulfate?
SO₄ ²¯
What does an ionic equation show?
Only the particles that react and the products they form
What do ionic equations not include?
The aqueous ions that are present on both sides of the equation
What must an ionic equation show on the compounds or elements?
Their ionic charges
What are hazard symbols?
Symbols that warn you about the dangers of a substance
What is a risk assessment?
Identifying the hazards their risks and suggest ways to reduce risks
When should a risk assessment be made?
Before the reaction
IN PERSON FLASHCARDS MADE FOR THE HAZARD SYMBOLS
Describe how the model of the atom has changed overtime
- John Dalton described atoms as solid spheres
- Plum pudding model - ball of positive charges containing small electrons
- Nuclear model - positive nucleus surrounded by a cloud of electrons and mostly empty space
- Bohr model - electrons orbit the nucleus in fixed shells
- Nucleus contains protons and neutrons
What is the relative mass and relative charge of protons,electrons and neutrons?
Relative charge | Relative mass |
————————————————
Protons | +1 | 1 |
Neutrons | 0 | 1 |
Electrons | -1 | 0.0005 |
Do atoms have a charge or no? Why?
No - they have the same number of protons and electrons so they cancel each other out
Where is most of the mass in an atom?
In the nucleus
What is a nuclear symbol used for?
Used to describe atoms
What is the bigger number on an element in the periodic table known as?
The mass number
What is the smaller number on an element in the periodic table known as?
The atomic number
What is the mass number equal to?
Mass number = number of protons + number of neutrons
What is the atomic number equal to?
Atomic number = the number of protons in an atom
What is the amount of protons in an atom equal to?
Number of protons = number of electrons
How to calculate number of neutrons using the mass number and atomic number?
Number of neutrons = mass number of - atomic number
How to calculate number of neutrons using the sum of number of protons and number of neutrons?
Number of neutrons = (protons + neutrons) - number of protons
What are elements?
Substances made up of atoms with the same number of protons
Why does each element have a unique atomic number?
As each element has a different number of protons
What is an isotope?
An atom of an element with the same number of protons but different number of neutrons
What is relative atomic mass (Ar)?
The average mass of one atom of an element, compared to 1/12 of the mass of one atom of carbon-12
How to calculate relative atomic mass (Ar)?
Ar = (mass x abundance) + (mass x abundance) / 100
How did Mendeleev originally group the periodic table?
Using the atomic mass of the elements - to group them by chemical properties
Why did Mendeleev swap some elements around?
When ordering by atomic mass didn’t fit the pattern of chemical properties
Why were some of the atomic masses on Mendeleevs table wrong?
He wasn’t aware of the presence of isotopes
Why did Mendeleev leave gaps in his periodic table?
To keep elements with similar properties together
What did Mendeleev predict the existence of? How?
Eka-silicon - used other elements in the columns to find gaps and predict
How is the modern periodic table organised?
By increasing atomic number
What are horizontal rows on the modern periodic table called?
Periods
What are vertical rows on the modern periodic table called?
Groups
What does the position of an element in the periodic table show you?
The number of electrons in their outer shell and how many shells they have
What does the group number tell you about the electronic configuration of an atom?
The number of electrons in the outer shell
E.g. group 7 like fluorine have 7 electrons in outer shell
What does the period number tell you about the electronic configuration of an atom?
The number of shells the atom has
What is the maximum electronic configuration possible?
2.8.8.2
What are the 2 ways electronic configurations can be shown?
- Diagrams and drawing the atom
- Through number e.g. 2.8.6
What is an ion?
A charged particle made when electrons are transferred
What type of electron transfer do metals have when they form ions?
They lose electrons and form positive ions
What is a cation?
Positive ion
What is an anion?
Negative ion
What does the charge on an ion show?
The number of electron gained or lost
What type of electron transfer do non metals have when they form ions?
They gain electrons to form negative ions
If an ion has a negative charge, what does this mean?
They have gained electrons - electrons have a negative charge so when they have more electrons than protons, they become negatively charged
If an ion has a positive charge, what does this mean?
They have lost electrons - electrons have a negative charge so when they less more electrons than protons, they become positively charged
What charge does each group have when become an ion?
Group 1: 1+
Group 2: 2+
Group 3: 3+
Group 4: varies, there’s no trend
Group 5: 3-
Group 6: 2-
Group 7: 1-
What is the way to find out the ionic formula of a compound if you have the ionic charges of each element?
Drag and drop method:
1. Find the ionic charges of each element using periodic table
2. Put the ionic charge of each element onto the other element
E.g. if it’s sodium sulphide:
1. Sodium has a charge of 1+ and sulfur has a charge of 2-
2. The ionic formula will therefore be Na₂S
If a compound ends in -ate what does this mean?
Oxygen and at least one other element are in the compound
If a compound ends in -ide what does this mean?
Only one element is in the compound
EXCEPT FOR HYDROXIDE IONS
What is an ionic bond?
The electrostatic attraction between oppositely charged ion
When are ionic bonds formed?
When electrons are transferred from metal atoms to non metal atoms
Is ionic bonding a transfer of electrons or when the atoms share electrons?
When electrons are transferred
How can ionic bonding and transfers be shown?
Dot and cross diagrams - one atom has dots and the other has crosses - the electrons are represented by the dot or cross
What does ionic bonding result in?
Charged ions when the electrons have been transferred
What are 3 properties of ionic compounds? Why?
- High melting and boiling points - lots of energy needed to overcome strong electrostatic forces of attraction between the ions
- Soluble in water
- Conduct electricity ONLY when they’re molten or dissolved - as ions are free to move and carry electric charge
Why are giant ionic lattices so strong?
The strong electrostatic forces of attraction between oppositely charged ions act in all direction - ions are closely packed
What are the 4 different models used to show the arrangement of atoms in a compound?
- Ball and sticks diagrams
- Dot and cross diagrams
- Displayed formula (2D)
- 3D model
What do ball and stick diagrams not show?
Which atoms the electrons in the bonds come from
They aren’t to scale and have gaps between ions when used to show lattices
What do dot and cross diagrams not show?
Relative sizes of atoms or their arrangement in space
What does the displayed formula (2D) not show?
The 3D structure or sizes of atoms
What’s the only thing the 3D model shows?
Outer layer
What is a covalent bond?
A shared pair of electrons between two non metal atoms
What is a covalent bond between?
Two non mental atoms
Is covalent bonding a transfer of electrons or when the atoms share electrons?
The share of electrons
What are simple molecular substances made up of?
Molecules containing a few covalently bonded atoms
What is the size of a simple molecule?
Around 10^-10 m
Are covalent bonds between atoms strong or weak in covalently bonded atoms?
They are strong between atoms
Are intermolecular forces between molecules strong or weak in covalently bonded atoms?
Forces between molecules are weak
What does a covalent bond result in? How?
A full outer shell for all of the atoms - they share electrons to have a full shell
What does a ionic bond result in? How?
A full outer shell for all of the atoms - they loss or gain electrons from each other to have a full shell
What are the 3 properties of simple molecular substances?
- Low melting and boiling points - mostly gases and liquids at room temperature - due to having weak forces in between the molecules
- Don’t conduct electricity - there are no charged particles in the substance to carry charge
- Some are soluble in water but some aren’t
What are giant covalent structures?
Solids containing atoms which are all bonded to each other by strong covalent bonds
What are 3 properties of giant covalent structures? Why?
- High melting and boiling points - lots of energy is required to overcome strong covalent bonds
- Don’t conduct electricity (with a couple exceptions) - no charged particles to carry charge
- Not soluble in water
What are examples of giant covalent structures?
Diamond and graphite
What are polymers?
Very long chains of covalently bonded carbon atoms
What are the bonds between the atoms in polymers?
Strong covalent bonds
What are polymers a collection of?
Monomers
How are polymers written?
Poly(the compound)
E.g. poly(ethene)
What are the 3 carbon allotropes?
- Diamond
- Graphite
- Graphene
What is the bonding like in diamond?
Carbon atoms form 4 covalent bonds
What is the properties of diamond?
Very hard
What is the conductivity of diamond?
Doesn’t conduct electricity
What is the bonding like in graphite?
Carbon atoms form 3 covalent bonds
No covalent bonds between layers of graphite
What are the properties graphite?
Soft & slippery
What is the conductivity of graphite? Why?
Conducts electricity and thermal energy - each carbon atom in it has one delocalised electron
What are the uses of graphite?
Electrodes
Lubricant
What is the bonding like in graphene?
Carbon atoms form 3 covalent bonds
What are the properties of graphene?
Strong & light
What is the conductivity of graphene?
Conducts electricity - each carbon atom in it has one delocalised electron
What are properties of fullerenes?
Have a hollow shape and a large surface area
What are nanotubes?
Cylindrical fullerenes
What can nanotubes do? Why?
Conduct electricity - have delocalised electrons
What is a metallic bond?
Two or more metals
What are metallic bonds held by?
Strong electrostatic forces of attraction
What are the 6 properties of metals? Why?
- High melting and boiling points - a lot of energy is needed to overcome strong metallic bonds
- High density - ions are packed close together
- Not soluble in water
- Shiny appearance
- Good electrical conductors - delocalised electrons can carry charge
- Soft and malleable - layers in metals slide over each other
What happens to electrons in metallic bonding?
They lose electrons to gain a full outer shell
What are chemical properties of non metals?
Outer shells are over half filled
Gain electrons to get a full outer shell
What is relative formula mass (Mr)?
Sum of all the relative atomic masses of the atoms in the molecular formula (the sum of all of the mass numbers in the compound)
What is one mole equal to?
One mole = 6.02 × 10²³ particles of a substance
What is the Avogadro constant?
6.022 × 10²³
What is the mass (in grams) of one mole of an atom of an element equal to?
The mass in grams of one mole of an atom of an element = the Ar of the element
What is the mass (in grams) of one mole of a molecule of a compound equal to?
The mass in grams of one mole of molecules of a compound = the Mr of the compound
How to calculate the number of moles?
Number of moles = mass in g/Mr or Ar
How to calculate the number of particles in a mass?
Number of particles = number of moles x 6.022 × 10²³
How to balance equations using masses if you know the mass of reactants and products?
- Do mass/Mr to find the moles of each substance
- Divide each number of moles by the smallest number of moles calculated
- If the results aren’t in whole numbers, multiply them by the same number to make them whole
- Place these numbers at the front of the chemical formulas
What is a limiting reactant?
A reactant that gets completely used up in a reaction, so limits the amount of products formed when it’s been used up - leaving all other reactants in excess
What is concentration?
Amount of substance dissolved in a certain volume of solution
If the mass of solute in a reaction is increased, what happens to the concentration?
It increases
If the volume of solution in a reaction is increased, what happens to the concentration?
It decreases
How can concentration be calculated?
Concentration = mass of solute/volume of solution
What are the units for concentration?
g dm^-3
What is the empirical formula?
The smallest whole number ratio of atoms in a compound
What is the molecular formula?
The unsimplified version of the empirical formula
How can molecular formula be found from the empirical formula?
- Find the Mr of empirical formula
- Divided the Mr of the compound by the Mr of the empirical formula
- Multiply the atoms in empirical formula by the result
What equipment is needed for the empirical formula experiment?
A crucible on a gauze containing magnesium ribbon with a lid on it
A tripod to hold the gauze and crucible
A Bunsen burner
What 3 things need to be weighed in the empirical formula experiment?
- Empty crucible and its lid
- The crucible with the lid and the contents in it before heating it
- The crucible with the lid and the contents in it after heating it
How can the mass of magnesium be found from the empirical formula experiment?
Mass of magnesium = (mass of crucible and lid + contents before heating) - (mass of empty crucible and lid)
How can the mass of oxygen be found from the empirical formula experiment?
Mass of oxygen = (mass of crucible and lid + contents after heating) - (mass of crucible and lid + contents before heating)
How can the empirical formula be worked out from the empirical formula experiment?
- Divide the mass of each element by its Ar (work out moles)
- Divide each result by the smallest number calculate to get the smallest whole number ratio
- This will give you the number of atoms of each element in its empirical formula
How can the mass of a product formed from a given mass of a reactant be calculated?
- Write a balanced equation for the reaction
- Divide the mass of the reactant by its Mr to find the number of moles
- Use the balanced equation to find the number of moles of the product
- Multiplied this number of moles by the Mr of the product to work out its mass
What is conservation of mass?
The idea that no atoms are created or destroyed in a chemical reaction, so the total masses of reactants and products are equal
If a sealed reaction vessel is weighed before and after the reaction, what shouldn’t you see?
You shouldn’t see a change in mass - mass has been conserved as no reactants or products can escape
If an unsealed reaction vessel is weighed before and after the reaction, what could you see?
You may be able to see a change in mass - either a decrease or an increase in
When would you see a decrease in mass after a reaction has happened in an unsealed vessel? Why?
If a gas has been made during the reaction and has escaped the vessel - its mass is no longer accounted for as has escaped
When would you see an increase in mass after a reaction has happened in an unsealed vessel?
If a gas from the air is a reactant in the reaction - its mass has thus been added to the mass in the vessel
What are the uses of diamond?
Cutting tools
