AS - Unit 1 - Atoms and reactions Flashcards by Allix Blackburn

Who devised the plumb pudding model for the early atom?

Joseph John Thomson

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How was the plumb pudding model believed to have looked?

Negatively charged particles within a ‘sea’ of positive charge

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Who proved the plumb pudding model wrong and devised the ‘nuclear atom’ theory?

Ernest Rutherford

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What results proved the nuclear atoms to be true?

Most of the particles were not deflected at all
A very small percentage of particles were actually deflected through large angles
A very few particles were actually deflected back towards the source

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Explain the structure of the ‘nuclear atom’ model.

The positive charge of an atom and most of mass in centre
Negative electrons orbit nucleus
Most of atoms volume would be in the space between the nucleus and the orbiting electrons
Overall neg and pos charges must balance

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What is the relative charge and mass of a proton?

Mass: 1.0
Charge: 1+

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What is the relative mass and charge of a neutron?

Mass: 1.0
Charge: 0

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What is the relative mass and charge of an electron?

Mass: 1/2000
Charge: 1-

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What do all isotopes of the same element have?

Different masses
Same no. Of protons and electrons
Different number of neutrons in nucleus

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Why do isotopes of the same element react in the same way?

Because chemical reactions involve electrons

Neutrons make no difference to chemical reactivity

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What is an ion?

Positively or negatively charged atom or (covalently bonded) group of atoms (a molecular ion)

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What is an isotope?

Atoms of the same element with different numbers of neutrons

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What is an atomic (proton) number?

The number of protons in the nucleus of an atom

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What is the mass (nucleon) number?

Number of particles (protons and neutrons) in the nucleus

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What is relative isotopic mass?

The mass of an atom of an isotope compared with one-twelfth of the mass of an atom of carbon-12

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What is relative atomic mass?

The weighted mean mass of an atom of an element compared with one-twelfth of the mass of an atom of carbon-12

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A sample of bromine contains 53.00% of bromine-79 and 47.00% of bromine-81. Determine the relative atomic mass of bromine and explain how to work it out

(53/100) X 79.00 + (47/100) X 81.00 = 41.87 + 38.07 = 79.94

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What is relative molecular mass?

The weighted mean mass of a molecule compared with one-twelfth of the mass of an atom of carbon-12

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What is relative formula mass?

The weighted mean mass of a formula unit compared with one-twelfth of the mass of an atom of carbon-12

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How do you calculate empirical formula?

mass divided by molar mass of both, divide by smallest number, find ratio and that is empirical

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What is the empirical formula?

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

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What is a molecule?

a small group of atoms held together by covalent bonds

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What is a molecular formula?

the actual number of atoms of each element in a molecule

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How do you calculate the molecular formula when given the empirical formula?

find the empirical formula mass, divide relative molecular mass by empirical formula mass. If whole answer is 4 for example there would be 4 lots of the empirical formula, meaning you times everything in the empirical formula by 4

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what is the molar volume?

volume per mol of a gas. at RTP molar volume is 24dm3mol-1 | so 1 mol of any gas takes up 24dm3mol-1 of space

how do you calculate the moles of gas?

volume/24 in dm3 | volume/24,000 in cm3

what is the definition of concentration?

the amount of solute, in mol, dissolved per 1 dm3 (1000cm3) of solution

how do you calculate amount of moles in a solution?

concentration of solute X volume of solution (in dm3)

what is a standard solution?

A solution of a known concentration (often used in titrations to determine unknown info about another substance)

Give 5 steps to making a standard solution

1. weigh out solute 2. completely dissolve solute in water in a beaker. transfer solution to flask, repeatedly rinsing out beaker and adding rinsings to the flask 3. add water to flask, not all the way up to the graduation line tho 4. carefully add water drop by drop to the line on the flask. line up the bottom of the meniscus exactly with the graduation line on the flask 5. put a stopper on the flask and invert several times

what is a species?

any type of particle that takes part in a chemical reaction

give three examples of a giant ionic compound

NaCl CaCl2 Mg(OH)2

Give an example of a giant covalent structure

SiO2

What ELEMENTS have giant structures?

all metals C Si B

what is stoichiometry?

the molar relationship between the relative quantities of substances taking part in a reaction

What are the three ways you can calculate amount in moles?

From mass ; Mass/molar mass From gas volumes ; V (in dm3) / 24 From solutions ; conc X volume

what is an acid

a proton donor

what is a base

a proton acceptor

what is an alkali

a type of base that dissolves in water forming hydroxide ions OH-

Give an equation for ammonia to show that it is a weak base

NH3 (aq) + H2O (l) NH4+ (aq) + OH- (aq)

what is a carboxyl acid group?

COOH

what is an amino basic group?

NH2

what is a salt?

any chemical compound formed from an acid when a H+ ion from the acid has been replaced by a metal ion or another positive ion, such as the ammonium ion, NH4+

what is a cation?

a positively charged ion

what is an anion?

a negatively charged ion

give the ionic equation for: | 2HCl (aq) + CaCO3 (s) --------> CaCl2 (aq) + H2O (l) + CO2 (g)

2H+ (aq) + CaO3 (s) ---------> Ca 2+ (aq) + H2O (l) + CO2 (g)

Give the ionic equation for: | 2HCl (aq) + CaO (s) ---------> CaCl2 (aq) + H2O (l)

2H+ (aq) + CaO (s) ----------> Ca 2+ (aq) + H2O (l)

Give the ionic equation for: | HCl (aq) + NaOH (aq) ----------> NaCl (aq) + H2O (l)

H+ (aq) + OH- (aq) ----------> H2O (l)

Acid + carbonate =

salt + CO2 + H2O

Acid + base =

Salt + water

Acid + alkali =

Salt + water

When are ammonium salts formed?

when acids are neutralised by aqueous ammonia

What does the word hydrated refer to in a crystalline compound?

It refers to the crystalline compound containing water molecules.

What does the word anhydrous refer to?

A substance that contains no water molecules

What does water of crystallisation mean?

Refers to water molecules that form an essential part of the crystalline structure of a compound

how can you use an experiment to work out the water of crystallisation in a hydrated salt?

weigh the hydrated salt heat the hydrated salt for ages weight the anhydrous salt find the weight difference (i.e. loss of water) calculate moles of anhydrous salt then calculate amount in moles of water find ratio of moles and the ratio will show amount of water

how do you calculate an unknown concentration from a titration? e.g. in a titration 25.0cm3 of 0.150 mol dm-3 sodium hydroxide NaOH(aq) reacted exactly with 23.40cm3 of sulfuric acid, H2SO4

calculate amount in moles of NaOH that reacted calculate amount in moles of H2SO4 that was used (by stoichiometry) calculate concentration in mol/dm3 of the sulfuric acid

how do you calculate an unknown molar mass from a titration? e.g. student dissolved 2.794g of acid HX in water and made solution up to 250cm3. student titrated 25cm3 of HX solution against 0.0614 mol/dm3 sodium carbonate Na2CO3(aq). 23.45cm3 of Na2CO3(aq) were needed to reach the end point.

calculate moles of Na2CO3 that reacted calculate moles of HX used in experiment based on molar ratios calculate amount in moles used to make up 250cm3 e.g. 25cm3 HX contains 2.88 X10-3 mol so 250cm3 contains 2.88 X10-2 mol calculate concentration in g/mol e.g. 2.794g/2.88 X10-2 = 97.0 g/mol

What is an oxidation number?

A measure of the number of electrons that an atom uses to bond with atoms of another element

when bonded with fluorine, what oxidation number does oxygen have?

When in a peroxide what oxidation number does oxygen have?

-1

What do oxidation number apply to?

Each atom

What is an oxyanion?

Negative ions that contain an element along with oxygen

What is oxidation?

A loss of electrons or an increase in oxidation number

What is reduction?

A gain of electrons or a decrease in oxidation number

What is a reducing agent?

A reagent that reduced (adds electrons to) another species

What is an oxidising agent?

A reagent that oxidises (takes electrons from) another species

What is the name of the reaction in which both reduction and oxidation take place?

A redox reaction

In the reaction Mg + Cl2 -----> MgCl2 what species is the reducing agent and which is the oxidising agent?

Mg is the reducing agent: it has reduced the Cl2 to 2Cl- by donating its electrons Cl2 is an oxidising agent: it has oxidised Mg to Mg2+ by removing its electrons

Which type of element tend to be reduced?

non-metals - they gain electrons to form negative ions

Which type of element tend to be oxidised?

metals - they lose electrons to form positive ions

What is reduction in terms of oxidation numbers?

Decrease in oxidation number

What is oxidation in terms of oxidation numbers?

An increase in oxidation number

What is the oxidation number of an atom?

ZERO

metal + acid =

salt + H2