Groups in the periodic table Flashcards
What do the elements in groups and periods share?
Chemical and physical properties
What is group 1 called?
Alkali metals
What are some chemical properties of alkali metals?
They’re malleable and conduct electricity (same as usual metals)
What properties do alkali metals have that make them unique?
- Relatively low melting points
- Soft and easily cut
What is the reactivity of alkali metals?
High reactivity and readily form compounds with non-metals
What is the oxidation of alkali metals like?
Easily oxidised and burn brightly in air
What is the trend of reactivity in alkali metals?
Increases down the group
What are the products of a alkali metal and water reaction?
Metal hydroxide (an alkali) and hydrogen
Explain why the reactivity increases down the alkali metals group
- Each element has one electron in its outer shell
- The period number is how many electron shells the element has
- The force between the outer electron and nucleus become weaker further down the group due to a larger gap between them
- The further the outer electron is to the nucleus, the easier it is to lose it to form a compound with another element
What are group 7 elements called
The halogens
What are all halogens?
Diatomic
Are halogens good or bad conductors of heat and electricity and why?
Bad, they’re non-metallic
Why does care need to be taken with halogens
They’re all corrosive and toxic
What is the trend for melting, boiling points and densities in halogens
They all increase down the group
What is the appearance of chlorine, bromine and iodine?
Chlorine- green gas
Bromine- brown liquid
Iodine- purple/brown solid
What do halogens form when reacting with metals?
They form salts that contain halide ions
Give some uses of halide salts
Sodium chloride- table salts
Sodium fluoride- used in toothpaste
Sodium bromide- used as a disinfectant in pools
Sodium iodide- added in salts to prevent iodine deficiency
What can all halogens be used as?
Disinfectants and bleaches - as they kill microorganisms and remove colour
What is the test for chlorine?
Damp blue litmus paper dipped in chlorine gas, if it turns red and then bleaches white
What does a reaction between hydrogen and a halide form?
A hydrogen halide (u wouldn’t think…) which dissolves in water to form an acidic solution
Give an explanation of the reaction between hydrogen and chloride
- Hydrogen and chlorine molecules collide and the covalent bonds holding the chlorine atoms together breaks
- The chlorine and hydrogen atoms covalently bond to form hydrogen chloride
- When the hydrogen chloride is placed in water, the bonds break in Cl- and H+ meaning the solution is now acidic due to the H+
What is the trend in reactivity for halogens?
Decrease going down the group
What is a displacement reaction
A more reactive element takes the place of a less reactive element in an ionic compound
What can displacement reactions be used for?
Finding out the reactivity order in a group
Explain why the reactivity of halogens decreases down the group
- Down the group, the distance between the outermost shell containing electrons and the nucleus increases
- Meaning the force of attraction between the positive nucleus and the incoming negative electron (gains one electron when reacts) decreases
- So the ions do not form as readily and reactivity decreases
What is oxidation in terms of electrons?
Loss of electrons (OILRIG)
What is reduction in terms of electrons?
Gain of electrons (OILRIG)
When do oxidation and reduction occur
At the same time in displacement reactions making them redox reactions
Why does oxidation and reduction have to occur at the same time?
Because the electrons lost from one element, needs to be gained by another
What are group 0 elements called?
Noble gases
Give three properties of noble gases
- colourless
- very low melting and boiling points
- poor conductors of electricity and heat
What does inert mean and how does this tie in with noble gases?
Unreactive, and all of the noble gases are inert
What is the trend of density, melting point and boiling point in noble gases
They increase down the group
Why were noble gases hard to find?
Because they don’t react with anything, they exist as single atoms
How much of the noble gases are there in our atmosphere?
Very minuscule
What is Krypton used in?
Photography lighting due to its brilliant white light when electricity is passed through it
What is Argon used in?
It’s denser than air so it’s added to the space above the wine in wine barrels to stop the oxygen in the air from reacting with the wine
What is Helium used in?
Helium has a very low density and is non-flammable and so is used in weather balloons and airships
What is Neon used in and why?
Long-lasting illuminated light signs because it produces a distinctive red-orange colour when electricity is passed through it
Why are noble gases unreactive?
Noble gases are already stable because they already have a full outer shell of electrons and so do not need to gain or lose any to become stable
What is the rate of reaction?
The rate at which reactants are turned into products
How can you control the rate of reactions?
Using variables (e.g concentration)
What do you need to measure to investigate the reaction rates?
How the reactants or products change with time or measuring the mass changes in the reactants or products
Why are reaction rates usually the fastest at the beginning of a reaction?
That is when the concentration of the reactants is highest
How do you know a reaction is faster based on a graph?
It will have a steeper gradient
Only when can chemical reactions occur?
When the reactant particles collide with enough energy to react
What is the activation energy
The minimum amount of energy needed for a reaction to occur
What happens in successful collisions?
The activation energy helps to break bonds so the atoms can be rearranged to make new substances (the products)
What happens when methane and air mix
Nothing until a spark or flame provides the energy for a reaction. The reaction then keeps going until it releases energy, which then provides the activation energy
What is an exothermic change
A reaction that releases energy
What reactions will not continue unless energy is constantly being supplied to it?
Endothermic changes
In general, when are reaction rates increased?
When the energy of the collisions and the frequency (the number of collisions in a certain set of time) increases
When do more collisions occur
When the particles are closer together and moving faster
How does concentration affect reaction rates?
Increasing the concentration of the solution increases the rate of reaction because there are more reacting particles in the same volume so collisions are more frequent
How does surface area affect reaction rates?
Increase the surface area to volume ratio, and the reaction rate increases because there is more surface area for collisions to happen o they’re more often
How does gas pressure affect reaction rates?
Increasing the gas pressure increases the rate of reaction because the reactant particles are squeezed closer together so collisions are more often
How does temperature affect reaction rates?
Increasing the temperature increases the reaction rate because the reactant particles speed up and have more energy and so, therefore, collide more often
What are catalysts
Substances that speed up reaction rates without affecting themselves and altering the products of the reaction
Why do catalysts save money in the industry world?
They make products faster and allow reactions to occur at a lower temperature
Why do catalysts never get replaced?
Because they’re never used up
What are reaction profiles used for?
Comparing catalytic and noncatalytic reactions
Why are more collisions successful with a catalyst?
Because the catalyst does not actually alter the energy change between the reactants and products, but because less energy is needed to start the reaction, there is more energy and so there are more collisions
What catalysts are used in catalytic converters in car exhausts and what do they do?
Platinum and palladium - lower the energy needed to convert harmful gases into harmless gases
How is an alcohol made?
An enzyme in yeast catalyses the reaction of glucose into ethanol and carbon dioxide
How does a reaction profile work?
Shows the energy change in a reaction. the energy stored in bonds is represented by a horizontal line, the greater the energy stored, the higher the line (refer to a diagram in case it comes up)
What happens to the energy in a reaction
It is transferred to the surroundings (usually by heating esp in solutions)
How would you know if a reaction is exothermic or endothermic
Temperature increases in exothermic
Temperature decreases in endothermic
What ‘thermic’ is precipitation reactions?
Endothermic or exothermic, depending on the substances involved
Give two examples of reactions that are always exothermic
- Displacement
- Neutralisation
How much activation energy is needed for neutralisation and precipitation reactions?
Very little as the reactions start as soon as the reactants are mixed
What reaction requires a higher activation energy
Combustion reactions
What thermic is breaking and making bonds
Breaking - endothermic (energy transferred to reactants to break their bonds)
Making- exothermic (energy transferred to surroundings as bonds form)
What is bond energy
The amount of energy needed to break a particular bond measured in Kilojoules per mole - kJ/mol
What are the bond energies for the following bonds: C-O C-H H-H O-H O=O C=O
C-O 358 C-H 413 H-H 436 O-H 464 O=O 498 C=O 805
How do you work out bond energy change
ITS NOT HARD I PROMISE, YOU JUST NEED TO GO AND SEE ON ACTIVE LEARN PAGE 147 BECAUSE I WONT EXPLAIN IT VERY WELL ON HERE :)
