Atomic Structure (Edexcel IGCSE Science (Double Award): Chemistry): Flashcards
Exam code: 4SD0
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What is an atom?
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What is an atom?
An atom is the smallest particle of an element, containing electrons surrounding a nucleus that contains protons and neutrons.
True or False?
Protons and neutrons are found in the nucleus of an atom.
True.
The nucleus is at the centre of the atom and contains protons and neutrons. Electrons orbit the nucleus in shells.
What is a molecule?
A molecule is a group of two or more atoms covalently bonded together. Molecules can be made of atoms of the same element (e.g. O2) or different elements (e.g. H2O).
What are the relative masses and charges of a proton, neutron and electron?
A proton has relative mass 1 and charge +1. A neutron has relative mass 1 and charge 0. An electron has negligible mass and charge −1.
The atomic number of an element is equal to the number of .......... in the nucleus, which in a neutral atom also equals the number of ...........
The atomic number of an element is equal to the number of protons in the nucleus, which in a neutral atom also equals the number of electrons.
What is the mass number of an atom?
The mass number is the total number of protons and neutrons in the nucleus of an atom.
True or False?
Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons.
True.
Isotopes share the same atomic number (same number of protons) but differ in mass number because they have different numbers of neutrons.
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. For example, lithium (atomic number 3, mass number 7) has 7 − 3 = 4 neutrons.
Electrons move around the nucleus in orbital paths called .........., and the mass of an electron is described as .......... because it is approximately 2000 times smaller than a proton.
Electrons move around the nucleus in orbital paths called shells, and the mass of an electron is described as negligible because it is approximately 2000 times smaller than a proton.
What is the relative atomic mass (Ar) of an element?
Relative atomic mass (Ar) is the average mass of one atom of an element, taking into account the abundance of all its isotopes, measured relative to 1/12th the mass of a carbon-12 atom.
What is relative atomic mass (Ar)?
Relative atomic mass (Ar) is the average mass of one atom of an element, calculated from the mass numbers and percentage abundances of all its isotopes.
What is the formula for calculating relative atomic mass from two isotopes?
The relative atomic mass is calculated as: Ar = [(% of isotope A × mass of isotope A) + (% of isotope B × mass of isotope B)] ÷ 100. Additional isotopes extend the numerator in the same way.
To calculate Ar, multiply each isotope's .......... by its .........., add the results together, then divide by ...........
To calculate Ar, multiply each isotope's mass number by its percentage abundance, add the results together, then divide by 100.
A sample of rubidium contains 72% 85Rb and 28% 87Rb. What is the relative atomic mass of this sample?
The relative atomic mass = [(72 × 85) + (28 × 87)] ÷ 100 = (6120 + 2436) ÷ 100 = 85.6 (to 1 d.p.).
True or False?
Isotopes of the same element have the same mass number but different atomic numbers.
False.
Isotopes have the same atomic number (same number of protons) but different mass numbers because they differ in the number of neutrons.
How can you recognise isotopes from their notation?
Isotopes have the same element symbol but different mass numbers written as a superscript. For example, 63Cu and 65Cu are both isotopes of copper.
The relative atomic mass of an element is not a whole number because it is an .......... of the masses of all .......... of the element, weighted by their abundance.
The relative atomic mass of an element is not a whole number because it is an average of the masses of all isotopes of the element, weighted by their abundance.
True or False?
If an element has only one naturally occurring isotope, its relative atomic mass equals the mass number of that isotope.
True.
With only one isotope, the average is simply the mass number of that single isotope. There are no other abundances to weight.
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