atomic structure- chemistry
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40 Terms
What is an atom?
The smallest particle of an element that retains its chemical properties.
What are the three subatomic particles?
Protons, neutrons, and electrons.
What is the charge of a proton?
+1
What is the charge of a neutron?
0 (neutral)
What is the charge of an electron?
−1
Where are protons found?
In the nucleus.
Where are neutrons found?
In the nucleus.
Where are electrons found?
In shells (energy levels) around the nucleus.
What is the atomic number?
The number of protons.
What does the atomic number tell you?
Which element it is.
What is the mass number?
Protons + neutrons.
What are isotopes?
Atoms with the same number of protons but different numbers of neutrons.
Why do isotopes have different masses?
They contain different numbers of neutrons.
What is a relative atomic mass (Ar)?
The weighted average mass of naturally occurring isotopes.
What is an ion?
A charged particle formed by gaining or losing electrons.
What happens when an atom loses electrons?
It becomes a positive ion (cation).
What happens when an atom gains electrons?
It becomes a negative ion (anion).
What is electron configuration?
The arrangement of electrons in shells.
Why are outer-shell electrons important?
They determine chemical reactivity.
What is the Periodic Table arranged by?
Increasing atomic number.
Why do isotopes have identical chemical properties?
They have the same number of electrons and therefore the same electron configuration.
Explain why isotopes have different physical properties.
Different numbers of neutrons give different masses.
Why are electrons found in energy levels?
Electrons occupy fixed energy levels around the nucleus.
What happens when an electron absorbs energy?
It moves to a higher energy level.
What happens when an excited electron returns to a lower energy level?
It emits electromagnetic radiation (a photon).
Why does magnesium form Mg²⁺?
Losing two electrons gives it a full outer shell.
Why does chlorine form Cl⁻?
Gaining one electron completes its outer shell.
Why do atoms react?
To achieve a more stable electron arrangement.
Why are noble gases unreactive?
They already have full outer electron shells.
Why is first ionisation energy generally higher across a period?
Increased nuclear charge attracts electrons more strongly.
Why does first ionisation energy decrease down Group 1?
Outer electrons are further from the nucleus and more shielded.
What is shielding?
Inner electrons reduce the attraction between the nucleus and outer electrons.
Which isotope is used in carbon dating?
Carbon-14.
Why are radioactive isotopes useful medically?
They can be detected to diagnose or treat disease.
Define ionisation energy.
Energy required to remove one electron from one mole of gaseous atoms.
Why is the nucleus so dense?
Nearly all mass is concentrated there.
What evidence supports the nuclear model?
Rutherford’s alpha scattering experiment.
Why is atomic radius smaller across a period?
Greater nuclear attraction pulls electrons closer.
What is successive ionisation energy?
Energy needed to remove additional electrons.
Why is there a large jump in successive ionisation energies?
The next electron is removed from an inner shell.