Atomic Structure (AQA GCSE Combined Science: Synergy: Life & Environmental Sciences): Flashcards
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Define the plum pudding model of the atom.
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Define the plum pudding model of the atom.
The plum pudding model is a model of the atom proposed by J.J. Thomson in which the atom is a ball of positive charge with electrons embedded throughout it, like plums in a pudding.
What did Rutherford's gold foil experiment show about the structure of the atom?
Rutherford's gold foil experiment showed that atoms are mostly empty space with a tiny, dense, positively charged nucleus at the centre. Most alpha particles passed straight through the foil, but a small number were deflected or bounced back, which could not be explained by the plum pudding model.
True or False?
In the plum pudding model, the positive charge is concentrated in a tiny central nucleus.
False.
In the plum pudding model, the positive charge is spread throughout the whole atom, not in a nucleus. It was Rutherford's nuclear model that introduced the idea of a central nucleus.
Rutherford fired .......... at a thin sheet of gold foil and found that most passed straight through, but a few were .......... or bounced back.
Rutherford fired alpha particles at a thin sheet of gold foil and found that most passed straight through, but a few were deflected or bounced back.
Why did a small number of alpha particles bounce straight back in Rutherford's experiment?
A small number of alpha particles bounced back because they came very close to the nucleus — a tiny, dense region of positive charge at the centre of the atom. Since alpha particles are also positively charged, they were strongly repelled by the nucleus.
True or False?
In the nuclear model of the atom, electrons orbit the nucleus in fixed shells.
True.
After Rutherford's nuclear model was proposed, it was further developed to include the idea that electrons move around the nucleus in fixed shells (energy levels) at specific distances from the nucleus.
What is the nuclear model of the atom?
The nuclear model describes the atom as having a tiny, dense, positively charged nucleus at its centre, surrounded by electrons orbiting in the mostly empty space around it. This model replaced the plum pudding model after Rutherford's scattering experiment.
How did the discovery of the neutron improve our model of the atom?
The discovery of the neutron improved our model by explaining the atom's mass. The mass of protons alone was not enough to account for the total mass of the nucleus, so neutrons — particles with no charge but a relative mass of 1 — were added to the nuclear model.
What is the radius of an atom?
Radius of an atom is approximately 1 × 10-10 m, or 0.1 nanometres (nm). This makes atoms extremely small — millions could fit across the width of a full stop.
The radius of a typical atom is about .......... m, while the radius of its nucleus is about .......... m, making the nucleus roughly 10 000 times smaller than the atom.
The radius of a typical atom is about 1 × 10-10 m, while the radius of its nucleus is about 1 × 10-14 m, making the nucleus roughly 10 000 times smaller than the atom.
Where is almost all of an atom's mass concentrated, and why?
Almost all of an atom's mass is concentrated in the nucleus, because the nucleus contains protons and neutrons, each with a relative mass of 1. Electrons have a very small mass and orbit in the mostly empty space outside the nucleus.
True or False?
The nucleus is about the same size as the whole atom.
False.
The nucleus is about 10 000 times smaller than the whole atom. The atom is mostly empty space, with the nucleus occupying only a tiny central region.
Why do electrons contribute very little to the total mass of an atom?
Electrons contribute very little to an atom's mass because their relative mass is very small compared to that of a proton or neutron. Around 1840 electrons would be needed to equal the mass of just one proton.
True or False?
The radius of a typical atom is about 0.1 nm (1 × 10-10 m).
True.
Atoms have a radius of approximately 0.1 nanometres (1 × 10-10 m). This is an extremely small distance — tens of millions of atoms could fit across the width of a human hair.
What is a nanometre?
A nanometre (nm) is a unit of length equal to 1 × 10-9 m, or one billionth of a metre. It is commonly used to measure the size of atoms and molecules.
How does the size of the nucleus compare to the overall size of the atom?
The size of the nucleus compared to the overall atom is very small — the nucleus is about 10 000 times smaller than the atom. If an atom were the size of a football stadium, the nucleus would be no bigger than a small pea at the centre of the pitch.
The table below shows the properties of the three subatomic particles. Fill in the missing values.
Particle
Relative Mass
Relative Charge
Proton
Neutron
Electron
Particle
Relative Mass
Relative Charge
Proton
1
+1
Neutron
1
0
Electron
very small
−1
What is the atomic number of an element?
Atomic number is the number of protons in the nucleus of an atom of that element. It is unique to each element and determines where the element sits on the periodic table.
True or False?
A neutron has a relative charge of +1.
False.
A neutron has a relative charge of 0 (it is neutral). It is the proton that carries a relative charge of +1.
Why do atoms have no overall electrical charge?
Atoms have no overall electrical charge because the number of protons (each with a charge of +1) equals the number of electrons (each with a charge of −1). These opposite charges cancel out exactly, making the atom electrically neutral.
What is a proton?
A proton is a subatomic particle found in the nucleus of an atom. It has a relative mass of 1 and a relative charge of +1.
True or False?
All atoms of the same element have the same number of protons.
True.
The number of protons in the nucleus defines which element an atom belongs to. This is the atomic number, and it is unique to each element.
What does the atomic number of an element tell us?
The atomic number tells us the number of protons in the nucleus of each atom of that element. It is also equal to the number of electrons in a neutral atom, and it determines the element's position on the periodic table.
In a neutral atom, the number of .......... is always equal to the number of .........., so the overall charge is zero.
In a neutral atom, the number of protons is always equal to the number of electrons, so the overall charge is zero.
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 tiny and dense, and contains almost all of the atom's mass.
What is the mass number of an atom?
Mass number (also called the nucleon number) is the total number of protons and neutrons in the nucleus of an atom. Its symbol is A.
The number of neutrons in an atom = .......... − .......... .
The number of neutrons in an atom = mass number − atomic number.
What are isotopes?
Isotopes are atoms of the same element that have the same number of protons but a different number of neutrons. They have the same atomic number but different mass numbers.
True or False?
Isotopes of the same element have the same mass number.
False.
Isotopes of the same element have the same atomic number (same number of protons) but different mass numbers, because they have different numbers of neutrons.
Why do isotopes of the same element have identical chemical properties?
Isotopes of the same element have identical chemical properties because they have the same number of electrons, and it is electrons that determine how an atom reacts chemically. The different number of neutrons only affects the atom's mass, not its chemistry.
True or False?
The isotope C-14 contains 8 neutrons.
True.
C-14 has an atomic number of 6 (6 protons) and a mass number of 14. The number of neutrons = 14 − 6 = 8.
How do you find the number of neutrons in an atom from its nuclear symbol notation?
To find the number of neutrons, subtract the atomic number (number of protons, lower number) from the mass number (total nucleons, upper number). Neutrons = mass number − atomic number.
In nuclear symbol notation, the number written at the top left is the .......... and the number at the bottom left is the .......... .
In nuclear symbol notation, the number written at the top left is the mass number and the number at the bottom left is the atomic number.
The first electron shell can hold a maximum of .......... electrons, and the second shell can hold a maximum of .......... electrons.
The first electron shell can hold a maximum of 2 electrons, and the second shell can hold a maximum of 8 electrons.
What is an electronic configuration?
An electronic configuration is a notation showing the number of electrons in each shell of an atom, written as numbers separated by commas (e.g. 2,8,1 for sodium). It describes how electrons are arranged around the nucleus.
True or False?
The second electron shell can hold a maximum of 8 electrons.
True.
The first shell holds up to 2 electrons and the second shell holds up to 8 electrons. Once a shell is full, electrons begin to fill the next shell.
How does the number of outer shell electrons relate to the group number in the periodic table?
The number of outer shell electrons equals the group number for main group elements. For example, an atom in Group 7 has 7 electrons in its outer shell, while an atom in Group 1 has just 1 outer shell electron.
Chlorine has atomic number 17. Its electronic configuration is 2, .......... , .......... .
Chlorine has atomic number 17. Its electronic configuration is 2, 8 , 7 .
True or False?
Sodium (atomic number 11) has the electronic configuration 2,8,2.
False.
Sodium has 11 electrons. The correct electronic configuration is 2,8,1 — 2 in the first shell, 8 in the second, and 1 in the third shell.
How does the number of occupied shells in an atom relate to its period in the periodic table?
The number of occupied shells equals the period number. For example, sodium has the electronic configuration 2,8,1 — three occupied shells — so it is in Period 3.
What is the valence shell?
The valence shell is the outermost occupied electron shell of an atom. Atoms are most stable when the valence shell is completely full of electrons.
What is the electronic configuration of potassium (atomic number 19)?
The electronic configuration of potassium is 2,8,8,1. It has 19 electrons: 2 in the first shell, 8 in the second, 8 in the third, and 1 in the fourth shell.
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