Atomic structure (Edexcel IGCSE Chemistry (Modular): Unit 1): Flashcards
Exam code: 4XCH1
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Define atom.
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Define atom.
An atom is the smallest particle of an element, containing electrons surrounding a nucleus that holds protons and neutrons.
Define molecule.
A molecule is a group of two or more atoms chemically combined to form an identifiable unit that retains the properties and composition of the substance.
Where are protons and neutrons found in an atom?
Protons and neutrons are found in the nucleus, at the centre of the atom. The nucleus is positively charged.
True or False?
Electrons have a relative mass of 1, the same as protons.
False.
Electrons have a negligible relative mass (approximately 1/1840 of a proton). Only protons and neutrons have a relative mass of 1.
The three subatomic particles that make up an atom are .........., .......... and ...........
The three subatomic particles that make up an atom are protons, neutrons and electrons.
What is the atomic number of an element?
Atomic number is the number of protons in the nucleus of an atom. In a neutral atom, it also equals the number of electrons.
How do you calculate the number of neutrons in an atom?
The number of neutrons is calculated by subtracting the atomic number from the mass number: neutrons = mass number − atomic number.
What is the mass number of an atom?
Mass number is the total number of protons and neutrons in the nucleus of an atom.
Define isotope.
An isotope is one of two or more atoms of the same element that have the same number of protons but a different number of neutrons.
Complete the table of subatomic particle properties.
Particle
Relative Mass
Charge
Proton
Neutron
Electron
Particle
Relative Mass
Charge
Proton
1
+1
Neutron
1
0 (neutral)
Electron
1/1840 (negligible)
−1
What is relative atomic mass (Ar)?
Relative atomic mass (Ar) is the average mass of one atom of an element, taking into account the abundance of all its isotopes. It is relative to 1/12 the mass of a carbon-12 atom.
Why is the relative atomic mass of an element often not a whole number?
The relative atomic mass is an average that accounts for all the isotopes of an element and their relative abundances. If an element has isotopes with different masses, the average may fall between whole numbers.
To calculate Ar, multiply the mass of each .......... by its percentage .........., add the results together, then divide by ...........
To calculate Ar, multiply the mass of each isotope by its percentage abundance, add the results together, then divide by 100.
True or False?
Isotopes of the same element have different numbers of protons.
False.
Isotopes are atoms of the same element with the same atomic number (same proton count) but different mass numbers (different numbers of neutrons).
A sample of rubidium contains 72% 85Rb and 28% 87Rb. What is the relative atomic mass of this sample?
The relative atomic mass is calculated as:
Ar = [(72 × 85) + (28 × 87)] ÷ 100 = (6120 + 2436) ÷ 100 = 85.6
True or False?
The relative atomic mass of an element can be calculated using only one isotope.
False.
The relative atomic mass must account for all isotopes and their percentage abundances. Using only one isotope would give just the mass of that isotope, not a true average.
How do you recognise isotopes from their nuclear notation?
You can recognise isotopes by looking at their notation: they share the same chemical symbol but carry different mass numbers as superscripts. For example, 63Cu and 65Cu are both isotopes of copper.
Complete the table to show the calculation of Ar for rubidium.
Isotope
Mass Number
% Abundance
Contribution (mass × %)
85Rb
85
72
87Rb
87
28
Ar = total ÷ 100
Isotope
Mass Number
% Abundance
Contribution (mass × %)
85Rb
85
72
6120
87Rb
87
28
2436
Ar = total ÷ 100
85.6
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