An atom's atomic number ( Z ) is the number of protons in its nucleus, which equals the number of electrons in a neutral atom.

True or False? The nucleus of an atom has an overall negative charge.

False. The nucleus contains protons (charge +1) and neutrons (charge 0), giving it an overall positive charge. Electrons are found in orbitals around the nucleus.

Why do electrons not contribute to the mass number of an atom?

Electrons have a relative mass of approximately 1/1836 of a proton, too small to be counted. Only protons and neutrons (collectively called nucleons ) contribute to the mass number .

The number of neutrons in an atom can be calculated using: Number of neutrons = .......... − ..........

The number of neutrons in an atom can be calculated using: Number of neutrons = mass number − atomic number

The mass number ( A ) is the total number of protons and neutrons (nucleons) in the nucleus of an atom.

What are the relative charges of a proton , neutron and electron ?

A proton has a relative charge of +1 , a neutron has a relative charge of 0 and an electron has a relative charge of −1 .

True or False? Protons and neutrons have the same relative mass.

True. Both protons and neutrons have a relative mass of 1 . Electrons are approximately 1836 times lighter and are assigned a negligible relative mass.

In an atom, electrons are found in .......... around the nucleus, while protons and neutrons are found in the ..........

In an atom, electrons are found in orbitals around the nucleus, while protons and neutrons are found in the nucleus .

Isotopes are atoms of the same element with the same number of protons but a different number of neutrons , resulting in different mass numbers.

True or False? Isotopes of the same element have identical chemical properties.

True. Isotopes share the same electron configuration , and electrons determine how an atom takes part in chemical reactions . Differing numbers of neutrons do not affect reactivity.

Why does a positive ion (cation) have fewer electrons than the corresponding neutral atom?

A positive ion forms when an atom loses electrons. Each electron lost increases the positive charge by one, leaving fewer electrons than protons in the nucleus.

A negatively charged ion has .......... electrons than protons because it has .......... electrons to become charged.

A negatively charged ion has more electrons than protons because it has gained electrons to become charged.

How many electrons does a Mg 2+ ion (atomic number 12) have?

A Mg 2+ ion has 10 electrons . Magnesium has 12 protons and 12 electrons when neutral, but has lost 2 electrons to form the 2+ ion: 12 − 2 = 10 .

True or False? Isotopes of the same element have the same melting point.

False. Isotopes differ in the number of neutrons , giving them different masses. This leads to small differences in physical properties including melting point, boiling point and density.

The number of neutrons in an atom is calculated as: Number of neutrons = .......... − ..........

The number of neutrons in an atom is calculated as: Number of neutrons = mass number − atomic number

How is the notation carbon-14 interpreted?

Carbon-14 is an isotope of carbon with a mass number of 14 . Written as element name followed by a dash and the mass number , it indicates this isotope has 8 neutrons (14 − 6 = 8).

Define relative atomic mass ( A r )

The relative atomic mass ( A r ) is the weighted mean mass of all isotopes of an element relative to 1/12 of the mass of a carbon-12 atom.

True or False? The standard used for relative isotopic mass is 1/12 of the mass of a carbon-12 atom.

True. All relative mass values use the same reference: 1/12 of a carbon-12 atom, defined as exactly 12 atomic mass units .

Why is relative atomic mass ( A r ) described as a weighted mean ?

Most elements exist as a mixture of isotopes with different masses. The A r weights each isotope's mass by its relative abundance , so more abundant isotopes contribute more to the average.

Relative isotopic mass is the mass of an isotope relative to .......... of the mass of a carbon-12 atom.

Relative isotopic mass is the mass of an isotope relative to 1/12 of the mass of a carbon-12 atom.

Define relative formula mass ( M r )

The relative formula mass ( M r ) is the total relative mass of a compound, found by adding the A r values of all atoms in its formula. Used for ionic and giant structures. Relative molecular mass is used for molecular compounds.

True or False? "Relative formula mass" is the correct term to use for ionic compounds.

True. For compounds with giant structures such as ionic compounds, relative formula mass is preferred. Relative molecular mass is reserved for molecular compounds.

Calculate the M r of potassium carbonate, K 2 CO 3 . ( A r : K = 39.1, C = 12.0, O = 16.0)

M r of K 2 CO 3 = (2 × 39.1) + 12.0 + (3 × 16.0) = 78.2 + 12.0 + 48.0 = 138.2

To calculate the M r of a compound, .......... the relative atomic masses of all atoms present in its .......... .

To calculate the M r of a compound, add the relative atomic masses of all atoms present in its formula .

Define molecular ion (M + )

A molecular ion (M + ) is a positively charged species formed when a molecule loses an electron during mass spectrometry (M → M + + e − ). The highest m/z peak in a mass spectrum corresponds to the M + ion and gives the relative molecular mass of the compound.

True or False? The molecular ion peak in a mass spectrum gives the relative molecular mass of the compound.

True. The molecular ion (M + ) is the peak at the highest m/z value. This m/z value equals the relative molecular mass ( M r ) of the compound.

Why does the [M+1] peak in a mass spectrum increase in height with more carbon atoms ?

The [M+1] peak arises from the natural abundance of carbon-13 ( 13 C). Each additional carbon atom increases the probability that one of them is 13 C, so the [M+1] peak grows with carbon count.

The relative atomic mass of an element is calculated from a mass spectrum using: A r = (abundance 1 × .......... 1 + abundance 2 × mass 2 + ...) ÷ ..........

The relative atomic mass of an element is calculated from a mass spectrum using: A r = (abundance 1 × mass 1 + abundance 2 × mass 2 + ...) ÷ 100

A compound contains one chlorine atom . What is the ratio of its M + to [M+2] peaks?

The ratio is 3:1 . 35 Cl (M + ) is three times more abundant than 37 Cl ([M+2]). Only two isotope combinations are possible with one chlorine atom .

True or False? A compound containing two bromine atoms produces four molecular ion peaks.

True. Bromine has two isotopes, 79 Br and 81 Br, with approximately equal relative abundances. A compound with one bromine atom shows M + and [M+2] peaks in a ratio of 1:1 .

A compound containing two chlorine atoms shows M + , [M+2] and [M+4] peaks in the ratio .......... : .......... : ..........

A compound containing two chlorine atoms shows M + , [M+2] and [M+4] peaks in the ratio 9 : 6 : 1 .

What is the significance of a mass spectrum being described as a molecular fingerprint ?

Every compound produces a unique pattern of ion peaks in its mass spectrum. This pattern can be matched against a spectral database by computer to identify an unknown compound.

True or False? A compound containing two bromine atoms produces four molecular ion peaks.

False. Two bromine atoms produce three peaks: M + , [M+2] and [M+4], in a ratio of 1:2:1 . The three peaks arise from the combinations of 79 Br and 81 Br.

A LevelChemistryEdexcelFlashcards1. Physical ChemistryAtomic Structure

Atomic Structure (Edexcel A Level Chemistry): Flashcards

Exam code: 9CHO

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FrontStructure of the Atom
Define atomic number

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Cards in this collection (33)

Define atomic number
An atom's atomic number (Z) is the number of protons in its nucleus, which equals the number of electrons in a neutral atom.
True or False?
The nucleus of an atom has an overall negative charge.
False.
The nucleus contains protons (charge +1) and neutrons (charge 0), giving it an overall positive charge. Electrons are found in orbitals around the nucleus.
Why do electrons not contribute to the mass number of an atom?
Electrons have a relative mass of approximately 1/1836 of a proton, too small to be counted. Only protons and neutrons (collectively called nucleons) contribute to the mass number.
The number of neutrons in an atom can be calculated using:
Number of neutrons = .......... − ..........
The number of neutrons in an atom can be calculated using:
Number of neutrons = mass number − atomic number
Define mass number
The mass number (A) is the total number of protons and neutrons (nucleons) in the nucleus of an atom.
What are the relative charges of a proton, neutron and electron?
A proton has a relative charge of +1, a neutron has a relative charge of 0 and an electron has a relative charge of −1.
True or False?
Protons and neutrons have the same relative mass.
True.
Both protons and neutrons have a relative mass of 1. Electrons are approximately 1836 times lighter and are assigned a negligible relative mass.
In an atom, electrons are found in .......... around the nucleus, while protons and neutrons are found in the ..........
In an atom, electrons are found in orbitals around the nucleus, while protons and neutrons are found in the nucleus.
Define isotopes
Isotopes are atoms of the same element with the same number of protons but a different number of neutrons, resulting in different mass numbers.
True or False?
Isotopes of the same element have identical chemical properties.
True.
Isotopes share the same electron configuration, and electrons determine how an atom takes part in chemical reactions. Differing numbers of neutrons do not affect reactivity.
Why does a positive ion (cation) have fewer electrons than the corresponding neutral atom?
A positive ion forms when an atom loses electrons. Each electron lost increases the positive charge by one, leaving fewer electrons than protons in the nucleus.
A negatively charged ion has .......... electrons than protons because it has .......... electrons to become charged.
A negatively charged ion has more electrons than protons because it has gained electrons to become charged.
How many electrons does a Mg²⁺ ion (atomic number 12) have?
A Mg²⁺ ion has 10 electrons. Magnesium has 12 protons and 12 electrons when neutral, but has lost 2 electrons to form the 2+ ion: 12 − 2 = 10.
True or False?
Isotopes of the same element have the same melting point.
False.
Isotopes differ in the number of neutrons, giving them different masses. This leads to small differences in physical properties including melting point, boiling point and density.
The number of neutrons in an atom is calculated as:
Number of neutrons = .......... − ..........
The number of neutrons in an atom is calculated as:
Number of neutrons = mass number − atomic number
How is the notation carbon-14 interpreted?
Carbon-14 is an isotope of carbon with a mass number of 14. Written as element name followed by a dash and the mass number, it indicates this isotope has 8 neutrons (14 − 6 = 8).
Define relative atomic mass (A_r)
The relative atomic mass (A_r) is the weighted mean mass of all isotopes of an element relative to 1/12 of the mass of a carbon-12 atom.
True or False?
The standard used for relative isotopic mass is 1/12 of the mass of a carbon-12 atom.
True.
All relative mass values use the same reference: 1/12 of a carbon-12 atom, defined as exactly 12 atomic mass units.
Why is relative atomic mass (A_r) described as a weighted mean?
Most elements exist as a mixture of isotopes with different masses. The A_r weights each isotope's mass by its relative abundance, so more abundant isotopes contribute more to the average.
Relative isotopic mass is the mass of an isotope relative to .......... of the mass of a carbon-12 atom.
Relative isotopic mass is the mass of an isotope relative to 1/12 of the mass of a carbon-12 atom.
Define relative formula mass (M_r)
The relative formula mass (M_r) is the total relative mass of a compound, found by adding the A_r values of all atoms in its formula. Used for ionic and giant structures. Relative molecular mass is used for molecular compounds.
True or False?
"Relative formula mass" is the correct term to use for ionic compounds.
True.
For compounds with giant structures such as ionic compounds, relative formula mass is preferred. Relative molecular mass is reserved for molecular compounds.
Calculate the M_r of potassium carbonate, K₂CO₃.
(A_r: K = 39.1, C = 12.0, O = 16.0)
M_r of K₂CO₃ = (2 × 39.1) + 12.0 + (3 × 16.0) = 78.2 + 12.0 + 48.0 = 138.2
To calculate the M_r of a compound, .......... the relative atomic masses of all atoms present in its ...........
To calculate the M_r of a compound, add the relative atomic masses of all atoms present in its formula.
Define molecular ion (M⁺)
A molecular ion (M⁺) is a positively charged species formed when a molecule loses an electron during mass spectrometry (M → M⁺ + e⁻). The highest m/z peak in a mass spectrum corresponds to the M⁺ ion and gives the relative molecular mass of the compound.
True or False?
The molecular ion peak in a mass spectrum gives the relative molecular mass of the compound.
True.
The molecular ion (M⁺) is the peak at the highest m/z value. This m/z value equals the relative molecular mass (M_r) of the compound.
Why does the [M+1] peak in a mass spectrum increase in height with more carbon atoms?
The [M+1] peak arises from the natural abundance of carbon-13 (¹³C). Each additional carbon atom increases the probability that one of them is ¹³C, so the [M+1] peak grows with carbon count.
The relative atomic mass of an element is calculated from a mass spectrum using:
A_r = (abundance₁ × .......... ₁ + abundance₂ × mass₂ + ...) ÷ ..........
The relative atomic mass of an element is calculated from a mass spectrum using:
A_r = (abundance₁ × mass ₁ + abundance₂ × mass₂ + ...) ÷ 100
A compound contains one chlorine atom. What is the ratio of its M⁺ to [M+2] peaks?
The ratio is 3:1. ³⁵Cl (M⁺) is three times more abundant than ³⁷Cl ([M+2]). Only two isotope combinations are possible with one chlorine atom.
True or False?
A compound containing two bromine atoms produces four molecular ion peaks.
True.
Bromine has two isotopes, ⁷⁹Br and ⁸¹Br, with approximately equal relative abundances. A compound with one bromine atom shows M⁺ and [M+2] peaks in a ratio of 1:1.
A compound containing two chlorine atoms shows M⁺, [M+2] and [M+4] peaks in the ratio .......... : .......... : ..........
A compound containing two chlorine atoms shows M⁺, [M+2] and [M+4] peaks in the ratio 9 : 6 : 1.
What is the significance of a mass spectrum being described as a molecular fingerprint?
Every compound produces a unique pattern of ion peaks in its mass spectrum. This pattern can be matched against a spectral database by computer to identify an unknown compound.
True or False?
A compound containing two bromine atoms produces four molecular ion peaks.
False.
Two bromine atoms produce three peaks: M⁺, [M+2] and [M+4], in a ratio of 1:2:1. The three peaks arise from the combinations of ⁷⁹Br and ⁸¹Br.

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