Atomic Structure Flashcards
All 29 cards in this deck
Describe the structure of an atom.
A positively charged nucleus containing protons and neutrons, surrounded by negatively charged electrons.
True or false? The nucleus takes up most of the volume of an atom.
False. The nuclear radius is much smaller than the atomic radius, but the nucleus contains almost all of the atom's mass.
What is the typical size (order of magnitude) of the radius of an atom or small molecule?
About 1 × 10⁻¹⁰ m.
Roughly how many times bigger is the radius of an atom than the radius of its nucleus?
About 10 000 to 100 000 (10⁴ to 10⁵) times bigger.
What is the atomic (proton) number of an atom?
The number of protons in its nucleus.
What is the mass (nucleon) number of an atom?
The total number of protons and neutrons (nucleons) in its nucleus.
In a symbol written as ¹⁴₆C, what does each number tell you?
Top number = mass number (14); bottom number = atomic number (6).
How do you find the number of neutrons in a nucleus from its mass number and atomic number?
Number of neutrons = mass number − atomic number.
What are isotopes?
Atoms of the same element with the same number of protons but different numbers of neutrons.
True or false? Neutral atoms of two isotopes of the same element have different numbers of electrons.
False. They have the same number of electrons, because they have the same number of protons; only the neutron number differs.
What are the relative mass and relative charge of a proton?
Relative mass 1, charge +1.
What are the relative mass and relative charge of a neutron?
Relative mass 1, no charge (0).
What are the relative mass and relative charge of an electron?
Relative mass about 0 (1/1836), charge −1.
What are the relative mass and relative charge of a positron?
Relative mass about 0 (same as an electron), charge +1.
How do electrons occupy the space around the nucleus of an atom?
They orbit the nucleus at different set distances (energy levels) from it.
What happens to an electron when it absorbs electromagnetic radiation?
It moves to a higher energy level, further from the nucleus.
What happens when an electron moves to a lower energy level, closer to the nucleus?
It emits electromagnetic radiation.
Why does an atom have no overall charge?
It has the same number of electrons as protons, so the negative and positive charges are equal.
How does an atom form a positive ion?
By losing one or more of its outer electrons.
What is the charge on an ion formed when an atom loses two outer electrons?
+2, because there are now two more protons than electrons.
True or false? An atom becomes a positive ion by gaining protons.
False. It loses outer electrons; the number of protons in the nucleus does not change.
Describe the plum pudding model of the atom.
A ball of positive charge with negative electrons embedded in it.
What were the results of Rutherford's alpha particle scattering experiment?
Most alpha particles passed straight through the foil, some were deflected, and a very few bounced straight back.
Why was the plum pudding model replaced after the alpha scattering experiment?
It could not explain the results; the new evidence showed the atom is mostly empty space with a tiny, dense, positively charged nucleus, so the model had to be changed.
True or false? A scientific model of the atom is changed or replaced when new experimental evidence cannot be explained by it.
True. Models are accepted only while they fit the evidence, so new results can force a change.
How did Rutherford know the nucleus must be positively charged?
Some positive alpha particles were pushed back (repelled) by it, and like charges repel.
What did Niels Bohr add to the nuclear model of the atom?
That electrons sit in fixed energy levels at set distances from the nucleus (the Bohr model).
True or false? Atoms of different elements can have the same positive charge on their nucleus.
False. Each element has its own characteristic nuclear charge, set by its number of protons.
How does the energy of an electron depend on how far its energy level is from the nucleus?
Electrons in levels further out have more energy than electrons in levels closer to the nucleus.