Atomic Structure Flashcards
All 30 cards in this deck
Describe the structure of an atom.
A positively charged nucleus containing protons and neutrons, surrounded by negatively charged electrons.
What is the typical size (order of magnitude) of an atom or small molecule?
About 1 × 10⁻¹⁰ m.
How does the radius of the nucleus compare with the radius of the whole atom?
The nuclear radius is much smaller — roughly 10 000 times smaller than the atomic radius.
True or false? The mass of an atom is spread evenly throughout its volume.
False. Almost all of the mass is concentrated in the nucleus.
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 in its nucleus.
What is the formula for the number of neutrons in a nucleus?
neutrons = mass number − atomic number
In the symbol ¹³₆C, what does each number tell you about the atom?
13 is the mass number and 6 is the atomic number, so the atom has 6 protons, 7 neutrons and 6 electrons.
What are isotopes?
Atoms of the same element with the same atomic number but a different number of neutrons.
True or false? Isotopes of an element have the same mass number but different numbers of neutrons.
False. They have the same atomic number and different numbers of neutrons, so their mass numbers differ.
Americium-241 has the symbol ²⁴¹₉₅Am. What must the symbol of another isotope of americium look like?
Same bottom number 95, different top number, e.g. ²⁴⁵₉₅Am.
What are the relative mass and relative charge of a proton?
Relative mass 1, relative charge +1.
What are the relative mass and relative charge of a neutron?
Relative mass 1, relative charge 0.
What are the relative mass and relative charge of a positron?
Relative mass 0.0005 (the same as an electron), relative charge +1.
Where are the electrons in an atom?
Orbiting the nucleus at different set distances (energy levels).
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 an orbit closer to the nucleus?
It emits electromagnetic radiation.
Why is an atom electrically neutral?
It has equal numbers of protons and electrons, so the positive and negative charges cancel.
What must a neutral atom lose to become a positive ion?
One or more of its outer electrons.
What is the charge on an ion formed when a neutral atom loses two outer electrons?
+2, because the atom now has 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 never changes when an ion forms.
Describe the plum pudding model of the atom.
A ball of positive charge with negatively charged electrons embedded in it, and no nucleus.
Give the three main observations of Rutherford's alpha particle scattering experiment.
Most alpha particles passed straight through the foil; some were deflected through small angles; very few were deflected through angles greater than 90°.
What conclusions about the atom were drawn from the alpha particle scattering results?
Atoms are mainly empty space, and there is a small, dense, positively charged nucleus containing most of the mass.
What did Bohr add to the nuclear model of the atom?
That electrons orbit the nucleus at set distances (fixed energy levels).
True or false? The nucleus of each element has a characteristic positive charge.
True. Every atom of an element has the same number of protons (the atomic number), so its nucleus always has that same positive charge.
What are the relative mass and relative charge of an electron?
Relative mass about 0.0005 (roughly 1/2000 of a proton), relative charge −1.
Why did Rutherford conclude that the nucleus must carry a positive charge?
Some alpha particles, which are positive, were pushed sharply away by the nucleus, and only like charges repel.
How can absorbing electromagnetic radiation turn an atom into a positive ion?
If an outer electron absorbs enough energy, it escapes from the atom completely, leaving the atom with more protons than electrons.
When an excited electron falls back to its original energy level, how much energy does the emitted electromagnetic radiation carry?
Exactly as much as the electron took in when it was excited: the energy gap between the two levels.