chemistry:module 2 ocr a chemistry

Define isotope

Atoms with the same number of protons and electrons but different number of neutrons

What are the differences between isotopes

• different number of neutrons

• Different mass numbers

• Different physical properties

Why do isotopes have the same chemical properties?

Isotopes of the same element have the same number of electrons on outer most shell/electon configuration

Define relative atomic mass

The weighted mean mass of an atom of an element compared to 1/12th the mass of one atom of carbon-12

Define relative isotopic mass

The mass of an isotope compared to 1/12th the mass of an atom of carbon-12

What is used to determine relative atomic mass

What is the first stage of determining mass using mass spectrometer

Ionisation - electron gun knocks out electrons to form positive ions

How would you work out abundance using triangle method

What is 1000mg equal to

What does concentration refer to?

The amount of solute, in moles, dissolved in each 1dm3 of a solution

What are some potential errors of using a gas syringe

• gas escape before bung is inserted

• Some gases are soluble in water so true amount no measured

What two errors in gas collection method could lead to inaccurate experimental values for %by mass of solid

• some gas is lost as the bung is replaced

• Some co2 dissolves in the water and therefore not collected

What could the experimental errors have an effect on in gas collection

• less co2 collected

• Smaller % by mass of solid

How can you modify gas collection method to give more accurate values

use gas syringe

Define empirical formula

The simplest whole number ratio of atoms of each element in a compound

How can you reduce % error in waters of crystallisation

• use a larger mass of crystals

• Use a more accurate balance (to 3/4/5 or more decimal places)

define salt

A substance in which the H+ has been replaced by a metal or an ammonium ion

Which is an example of a weak base

What state symbols would these have: NaOH, CaCl2, NH3

How to reduce % error in titration experiment

Increasing volume so use a larger flask (1000cm3)

What is a titration

A technique used to accurately measure the volume of one solution that reacts Exaclty with another solution. Used to find concentration

How would rinsing Pipette with water affect titre

Smaller titre (p= petite)

How would rinsing burette with water affect titre

Larger titre (b=big)

Lower concentration

Effect of leaving funnel in burette?

Small drops give lower titre volume

Why does adding distilled water to conical flask not affect titration

Used to wash sides of flask so all acid is reacted, does not affect titre as number of moles in acid remains the same

Why is there always a trial titre?

To estimate the titre volume

Why d you repeat titre?

To get concordant results

What does concordant results mean in titration

Results within ±0.10cm3 of each other

How to ensure accurate readings from burette?

1. Use a white tile

2. Ensure burette is upright

3. Read meniscus at eye level

4. Swirl conical flask

5. Remove funnn from top of burette

Why might there be a lower titre volume

Air bubble in Pipette

How to reduce % uncertainty in burette

• Increase volume and conc of substance in conical flask

• Decrease conc of substance in burette

What is another word for shells in electron configuration

Principle quantum number (n)

How can you figure out the number of electrons in each shell

2(n)²

What is an orbital

A region around the nucleus that can hold up to 2 electrons with opposite spins

what are the types of orbitals

• s

• P

• D

• F

What shape is s orbital

Spherical

How many p orbitals are there

3

What shape is a p orbital

Dumb-bell

Define ionisation energy

The energy needed to remove 1 mol of electrons from 1 mol of gaseous atoms to form 1 mol of gaseous 1+ ions

When writing ionisation energy equation, where does the 1st, 2nd, 3d IE go

What is the trend of IE down a group

• atomic radius increases

• More inner shells so shielding increases

• Nuclear attraction to outer electrons decreases

• First ionisation energy decreases

What is trend of IE across a group

• atomic radius decreases

• Nuclear charge increases

• Similar shielding

• Nuclear attraction increases

• First IE increases

What is drop 1 in ionisation energy and explain it

Be-B

• Be electron removed from 2s, B electron removed from 2p

• 2p has higher energy than 2s

What is drop 2 and explain

N-O

• Paired electrons in 2p orbital in oxygen repel so lower first IE

What is drop 3 and explain

Mg-Al

• Mg electron removed from 3s Al electron removed from 3p

• Al electron has a higher energy or 3p has higher energy than 3s

Why is 2nd IE greater thats first

• the proton:electron ratio increases

• There is greater nuclear attraction to outer most electrons

What is a giant ionic lattice

Repeating patterns of oppositely charged ions strongly attracted in all directions

Define covalent bonding

The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms

What type of attraction is in a covalent bond

Localised attraction

What is a lone pair of electrons

A pair of electrons that are not shared

What is expansion of the octet

When n=3

Define average bond enthalpy

Breaking of 1 mole of bonds in gaseous molecules

Define a dative bond

A covalent bond in which the shared pair of electrons is provided by one of the bonding atoms only

What is electron pair repulsion theory

• electron pair surrounding central atom repel each other

• Shape is determined by the number of bond pairs and lone pairs

2 pairs of electrons have Which shape

3 pairs is…

3 pairs (2BP+1LP) is…

Non linear - 118 degrees

4 pairs is…

Tetrahedral-109.5 degrees

4 pairs (3BP+1LP) is…

Trigonal pyramidal-107 degrees

4 pairs (2BP+2LP) is…

Non linear- 104.5 degrees