C3 Part A Flashcards
What are the two obvious ways to categorise elements?
- Their physical and chemical properties
- Their relative atomic mass
Why could scientists in the 1800s only rely on elements physical characteristics and atomic mass to classify them?
They had no idea of atomic structure (electrons, neutrons, protons) and relative atomic mass was the only characteristic they could measure
What was Newlands’ law of octaves?
Newland tried to arrange elements in a useful order in 1864, he noticed that every 8th element had similar properties to he listed the known elements in rows of seven.
Why were Newlands’ octaves criticised? (4)
- The pattern broke down on the third row due to transition metals
- His groups contained elements that didnt have similar properties (eg. carbon and titanium)
- He mixed up metals and non-metals (oxygen and iron)
- He didn’t leave any gaps for elements that hadn’t been discovered yet
How did Dmitri Mendeleev order elements in 1869?
He put them in order ot atomic mass and left gaps in order to keep elements with similar properties in the same vertical gaps. These gaps predicted the properties of undiscovered elements.
How is the modern periodic table arranged?
In vertical groups, with the group number being equal to the number of electrons in the outer shell of the element.
How does the distance between a nucleus and an electron affect an atoms reactivity?
The further away the electron is (the more ‘shells’/energy levels are present), the more distance and therefore the less attraction there is between the electron and the nucleus. This means the electrons in the outer shell are more easily lost and the element is more reactive.
As you study down Group 1 of the periodic table, how are reactivity and boiling/melting points impacted?
The alkali metals become more reactive (the electron is more easily lost because it’s further from the nucleus) and the elements will have lower melting and boiling points.
Name the 6 alkali (group 1) metals and their chemical symbols
Lithium Li
Sodium Na
Potassium K
Rubidium Rb
Caesium Cs
Francium Fr
What do all the group 1 metals have in common?
They have one electron in their outer shell and are very reactive
What do alkali (group 1) metals form when reacted with non-metals?
Ionic compounds
Explain why ionic compounds are formed from group 1 metals and a non metal and what is produced from this reaction
The electron in the highest energy level of the group 1 metal atom is weakly bonded to the nucleus, this means that covalent bonding can’t occur because the atom needs to form a 1+ ion.
A white compound that dissolves in water to form a colourless solution is the product.
Give atleast one symbol equation example of a group 1 metal reacting with chlorine
- lithium + chlorine → lithium chloride
- 2Li(s) + Cl2(g) → 2LiCl(s)
- sodium + chlorine → sodium chloride
- 2Na(s) + Cl2(g) → 2NaCl(s)
- potassium + chlorine → potassium chloride
- 2K(s) + Cl2(g) → 2KCl(s)
What happens when lithium, sodium or potassium are reacted with water?
- They will float and move around on the surface, fizzing
- They produce hydrogen (remember the “squeaky pop” splint test)
- They form hydroxides that dissolve in water to make an alkaline solution
What is the balanced equation for sodium reacting with water?
2Na(s)+ 2H2O(l)→ 2NaOH(aq) + H2 (g)
What is the commonly used name for the Group 7 elements?
The Halogens
List the 5 elements in Group 7 and their symbols
- Fluorine F
- Chlorine Cl
- Bromine Br
- Iodine I
- Astatine At
As you study down Group 7 how do the characteristics of the elements change?
- They become less reactive
- Their melting and boiling points increase
Describe each of the halogens physical characteristics (colour etc) and molecular structure
- Fluorine is a reactive, poisonous yellow gas
- Chlorine is a fairly reactive, poisonous dense green gas
- Bromine is a dense, poisonous, red-brown volatile liquid
- Iodine is a dark grey crystalline solid or a purple vapour.
They are all non-metals that exist as molecules which are pairs of atoms.
What do halogens form when they are reacted with metals?
Ionic bonds, 1 -ions called halides
Fill in the gaps in this sentence:
A more reactive halogen will ……. a less reactive halogen from an …………. solution of its salt eg. Chlorine can displace ……… and iodine from an aqueous solution of its salt (a ……….. or ………..)
A more reactive halogen will **displace **a less reactive halogen from an **aqueous **solution of its salt eg. Chlorine can displace bromine and iodine from an aqueous solution of its salt (a bromide or iodide)
What is the balanced symbol equation for the reaction of chloring and potassium iodide?
Cl2 (g)+ 2KI (aq)→ I2 (aq)+ 2KCl (aq)
Give the 5 main properties of transition metals
- Good conductors of heat and electricity
- They’re very dense, strong and shiny
- Transition metals are much less reactive than Group 1 metals
- They’re denser, stronger and harder than Group 1 metals
- Transition metals and their compounds all make good compounds,
Transition metals often have more than one ion (eg. Fe2+and Fe3+). What do these usually form?
Different coloured compounds (eg. Fe2+ ions give green, whereas Fe3+ make a red/brown compound, such as rust)
Colours in gemstones such as blue sapphires and green emeralds are due to transition metals.
Name 3 transition metal catalysts and how they are used
- Iron is the catalyst used in the Haber process for making ammonia
- Manganese (IV) oxide is a good catalyst for the decomposition of hydrogen peroxide
- Nickel is useful for turning oils into fats for making margarine
When you lather hard water and soft water with soap, what is the difference in what happens?
With soft water, you get a nice lather but hard water creates a nasty scum - unless you’re using a soapless detergent.
Why does hard water create scum when mixed with soap, rather than a lather as soft water does?
There are dissolved calcium and magnesium ions in the water that react with the soap to make scum which is insoluble.
What happens when hard water is heated?
It will form a scale (mostly calcium carbonate)
How does scale impact on heating systems?
Badly scaled up pipes and boilers reduce the efficency of heating systems, and may need to be replaced - all of which costs money.
How does scale reduce the efficency of a kettle?
It acts as a slight thermal insulator, meaning that if scale builds up on the heating element of a kettle, the water will take longer to boil that a non-scaled up kettle. This reduces efficency.
How might rainfall become hard water?
It falls on some types of rocks (e.g. limestone, chalk and gypsum) and can dissolve in compounds like magnesium sulfate (soluble) and calcium sulfate (slightly soluble).
