Atomic Structure (OCR GCSE Chemistry A (Gateway)): Flashcards
Exam code: J248
1/300Still learning
Know0
What is the plum pudding model of the atom?
Was this flashcard helpful?
Cards in this collection (30)
What is the plum pudding model of the atom?
The plum pudding model is J.J. Thomson's model of the atom, in which negative electrons are spread throughout a soft sphere of positive charge, like plums in a pudding. It was proposed in 1897.
What is an atom?
An atom is the smallest part of an element that retains the chemical properties of that element. Atoms are the building blocks of all matter.
Define atomic number (proton number).
Atomic number (symbol Z) is the number of protons in the nucleus of an atom. It is unique to each element and also equals the number of electrons in a neutral atom.
What were the three key ideas in John Dalton's atomic theory (1803)?
Dalton's three key ideas were:
Matter is made of atoms that cannot be created, destroyed or divided
Atoms of the same element are identical; atoms of different elements are different
Different atoms combine to form new substances
Name the three subatomic particles and state where each is found in the atom.
The three subatomic particles are:
Protons: found in the nucleus
Neutrons: found in the nucleus
Electrons: found in shells around the nucleus
Define mass number (nucleon number).
Mass number (symbol A) is the total number of protons and neutrons in the nucleus of an atom. Subtracting the atomic number from the mass number gives the number of neutrons.
What did Rutherford's gold foil experiment show, and how did it change the atomic model?
The gold foil experiment showed that some positively charged particles were scattered or deflected back, proving that most of an atom's mass is concentrated in a small, dense, positive nucleus. This replaced the plum pudding model with the nuclear model.
Complete the table of subatomic particle properties.
Particle
Relative mass
Relative charge
Proton
1
+1
Neutron
..........
..........
Electron
..........
..........
Particle
Relative mass
Relative charge
Proton
1
+1
Neutron
1
0
Electron
negligible
-1
Number of neutrons = .......... − ..........
Number of electrons (neutral atom) = ..........
Number of neutrons = mass number − atomic number
Number of electrons (neutral atom) = atomic number
True or False?
In Rutherford's nuclear model, electrons are embedded within a sphere of positive charge.
False.
In the nuclear model, the positive charge is concentrated in a central nucleus, with electrons orbiting around the outside. This is the key difference from the plum pudding model, where positive charge was spread throughout.
True or False?
Most of an atom's mass is found in the nucleus.
True.
Protons and neutrons are both located in the nucleus and each have a relative mass of 1. Electrons have negligible mass and orbit outside the nucleus, so virtually all the atom's mass is concentrated in the nucleus.
Define isotopes.
Isotopes are atoms of the same element that have the same number of protons and electrons but a different number of neutrons. They have the same chemical properties because they have the same electron configuration.
In 1913, Niels Bohr proposed that electrons orbit the nucleus in fixed .......... at set .......... from the nucleus, with higher energy orbitals located .......... from the nucleus.
In 1913, Niels Bohr proposed that electrons orbit the nucleus in fixed shells at set distances from the nucleus, with higher energy orbitals located further from the nucleus.
What is the approximate radius of an atom?
An atom has a radius of about 1 × 10-10 m (0.1 nm). Atoms are very small, but the atom is mostly empty space.
True or False?
Isotopes of the same element have the same chemical properties.
True.
Isotopes have the same number of electrons in their outer shells, and it is the electron configuration that determines chemical behaviour. The differing number of neutrons adds mass only and does not affect chemistry.
Why is it a fundamental feature of science that atomic models have changed over time?
Scientific models change over time because new experimental evidence can disprove existing models. When evidence no longer fits a model, scientists revise or replace it. The development of atomic models shows this process in action.
What is the nucleus of an atom?
The nucleus is the central region of an atom containing protons and neutrons. It is extremely small relative to the overall atom but contains virtually all of the atom's mass.
Beryllium has an atomic number of 4 and a mass number of 9. How many protons, neutrons and electrons does a neutral beryllium atom have?
A neutral beryllium atom has:
Protons: 4 (equal to the atomic number)
Electrons: 4 (equal to the atomic number for a neutral atom)
Neutrons: 5 (mass number − atomic number = 9 − 4)
What is the nuclear model of the atom?
The nuclear model is Rutherford's model of the atom, proposed in 1909, in which the atom consists mainly of empty space with a dense, positive nucleus at the centre and electrons orbiting around it.
Why is the mass of an electron described as negligible?
The mass of an electron is described as negligible because it is around 1836 times smaller than the mass of a proton or neutron. Electrons contribute so little to the total mass that they are assigned a relative mass of effectively zero.
Why does forming an ion change the number of electrons but not the number of protons?
Forming an ion involves gaining or losing electrons, which changes the overall charge. The number of protons is fixed by the element's identity and does not change in any chemical process. Only electrons are transferred.
What problem did Bohr's model solve that Rutherford's nuclear model could not explain?
Bohr's model explained why the atom does not collapse inwards due to the attraction between the positive nucleus and negative electrons. By placing electrons in fixed shells at set distances, Bohr showed they could orbit stably without falling into the nucleus.
True or False?
Electrons move in fixed paths called shells around the nucleus.
True.
Electrons are arranged in shells (also called energy levels) at set distances from the nucleus. Each shell can hold a fixed number of electrons.
An element X has a mass number of 63 and 34 neutrons. How many protons and electrons does a neutral atom of X have?
Using the formula: protons = mass number − neutrons = 63 − 34 = 29 protons. A neutral atom has equal protons and electrons, so it also has 29 electrons.
True or False?
J.J. Thomson discovered the electron in 1897 using a cathode-ray tube.
True.
Thomson used a cathode-ray tube to show that electrons are negatively charged subatomic particles. This proved that atoms are divisible and led to the plum pudding model.
Why are relative masses and charges used for subatomic particles rather than actual values?
Subatomic particles are so small that measuring their actual masses and charges in conventional units (such as grams or coulombs) is not practical. Relative masses and charges compare particles to each other, making the values easier to use.
True or False?
A Mg2+ ion has more electrons than a neutral magnesium atom.
False.
A Mg2+ ion has fewer electrons than a neutral magnesium atom. The 2+ charge means it has lost two electrons, leaving it with 10 electrons instead of 12.
Define isotopes.
Isotopes are atoms of the same element that have the same number of protons but a different number of neutrons. They have identical chemical properties but different masses.
What is an ion?
An ion is an atom or group of atoms that has an overall electrical charge, formed by gaining or losing electrons. A positive ion (cation) has lost electrons; a negative ion (anion) has gained electrons.
How does the size of the nucleus compare to the atom as a whole?
The nucleus is approximately 10 000 times smaller than the atom. This means the atom consists mostly of empty space.
Sign up to unlock flashcards
or