What does the electron-shell (Bohr) model show?
It shows that electrons orbit the nucleus in fixed energy levels or shells.
What particles are found in the nucleus of an atom?
Protons and neutrons.
What are electrons and where are they found?
Electrons are negatively charged particles found in shells around the nucleus.
What does each circle or shell represent in the electron-shell model?
Each shell represents an energy level where electrons move.
How many electrons can the first three shells hold?
1st: 2, 2nd: 8, 3rd: 8 (for the first 20 elements).
What are valence electrons?
The electrons in the outermost shell of an atom.
Why are valence electrons important?
They determine how an element reacts and bonds with other atoms.
What does a period (row) on the periodic table show?
The number of electron shells an element has.
What does a group (column) on the periodic table show?
The number of valence electrons in an atom.
Why do elements in the same group have similar properties?
They have the same number of valence electrons, so they react similarly.
Why do atoms form bonds?
To get a full outer shell of electrons (become stable).
What makes Group 1 elements very reactive?
They have 1 valence electron and easily lose it to form a full outer shell.
Why are Group 18 elements (noble gases) unreactive?
Their outer electron shells are already full.
What causes chemical properties to repeat in the periodic table?
The pattern of electron shells and valence electrons repeats.
Why is the periodic table called “periodic”?
Because similar properties repeat at regular intervals as shells fill up.
How does atomic number relate to electron arrangement?
As the atomic number increases, electrons fill shells in order (2, 8, 8…).
What happens when an outer shell is full?
A new shell begins, starting a new period on the periodic table.
Which electrons have the highest energy?
The ones farthest from the nucleus (in the outer shells).
What happens to an electron when it gains energy?
It moves to a higher energy level (outer shell).
What happens when an electron releases energy?
It falls back to a lower shell.
