What are the alkali metals and where are they found?
Answer: Group 1 elements (Li, Na, K, Rb, Cs, Fr) — very reactive metals that form +1 ions.
Explanation
Reactivity increases down the group.
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Chemistry: Atomic Structure and Periodic Trends (High School)
Periodic tableMolesBondingPeriodic trendsAtomic structureElectrons
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Periodic table
Why are the noble gases unreactive?
Answer: They have full valence shells (8 electrons, or 2 for helium).
Explanation
Group 18: He, Ne, Ar, Kr, Xe, Rn.
What are the halogens?
Answer: Group 17 elements (F, Cl, Br, I, At) — very reactive nonmetals that form −1 ions.
Explanation
Fluorine is the most reactive nonmetal.
What do elements in the same group have in common?
Answer: The same number of valence electrons, which gives them similar chemical properties.
Explanation
Example: all alkali metals (Group 1) have one valence electron.
How is the modern periodic table organized?
Answer: By increasing atomic number, with elements in columns (groups) having similar properties.
Explanation
Mendeleev's original table was ordered by atomic mass.
Moles
What is Avogadro's number and what does a mole represent?
Answer: 6.022 × 10^23; one mole is that many particles of a substance.
Explanation
The molar mass in grams equals the atomic/molecular mass in amu.
Bonding
What is a metallic bond?
Answer: Attraction between metal cations and a 'sea' of delocalized electrons.
Explanation
Explains conductivity, malleability, and luster of metals.
What is the octet rule?
Answer: Atoms tend to gain, lose, or share electrons to have eight valence electrons.
Explanation
Hydrogen is an exception, needing only two.
What makes a covalent bond polar?
Answer: A difference in electronegativity between the bonded atoms, so electrons are shared unequally.
Explanation
Example: the O–H bonds in water.
What is a covalent bond?
Answer: A bond formed when two nonmetals share one or more pairs of electrons.
Explanation
Single, double, and triple bonds share 1, 2, or 3 pairs.
What is an ionic bond?
Answer: A bond formed by the transfer of electrons from a metal to a nonmetal, creating attracting ions.
Explanation
Example: NaCl. Ionic compounds have high melting points and conduct when dissolved.
Periodic trends
Where are metals, nonmetals, and metalloids located?
Answer: Metals on the left and center, nonmetals on the upper right, metalloids along the staircase line between them.
Explanation
Metalloids: B, Si, Ge, As, Sb, Te.
How does metallic character trend on the periodic table?
Answer: Increases down a group and decreases across a period.
Explanation
Metals lose electrons easily; the most metallic elements are at the bottom left.
Why do cations have a smaller radius than their parent atoms?
Answer: Losing electrons reduces electron-electron repulsion and often removes an entire energy level.
Explanation
Anions are larger than their parent atoms for the opposite reason.
What is electronegativity and which element has the highest?
Answer: The ability of an atom to attract shared electrons; fluorine is highest (about 4.0).
Explanation
Increases across a period, decreases down a group; noble gases usually not assigned.
What is ionization energy and how does it trend?
Answer: The energy needed to remove an electron; it increases across a period and decreases down a group.
Explanation
Opposite of the atomic radius trend.
How does atomic radius change across a period and down a group?
Answer: Decreases across a period (left to right); increases down a group.
Explanation
Across: more protons pull electrons closer. Down: more energy levels are added.
Atomic structure
What are the three subatomic particles and their charges?
Answer: Protons (+1), neutrons (0), electrons (−1).
Explanation
Protons and neutrons are in the nucleus; electrons occupy orbitals around it.
How is average atomic mass calculated?
Answer: Weighted average of the isotope masses based on their natural abundances.
Explanation
Sum of (mass × fractional abundance) for each isotope.
What is an ion?
Answer: An atom that has gained or lost electrons and therefore has a net charge.
Explanation
Cations are positive (lost electrons); anions are negative (gained electrons).
What are isotopes?
Answer: Atoms of the same element with different numbers of neutrons.
Explanation
Example: carbon-12 and carbon-14.
What is the mass number?
Answer: The total number of protons plus neutrons in the nucleus.
Explanation
Mass number − atomic number = number of neutrons.
What does the atomic number tell you?
Answer: The number of protons in an atom, which identifies the element.
Explanation
In a neutral atom it also equals the number of electrons.
Electrons
What are valence electrons?
Answer: Electrons in the outermost energy level that participate in bonding.
Explanation
Main-group elements: the group number (1, 2, 13–18) gives 1, 2, 3–8 valence electrons.
What is the electron configuration of oxygen (Z = 8)?
Answer: 1s2 2s2 2p4
Explanation
Oxygen has 6 valence electrons (2s2 2p4).
State Hund's rule.
Answer: Electrons fill degenerate orbitals singly with parallel spins before pairing up.
Explanation
Think of bus seats: everyone takes an empty seat before sharing.
State the Pauli exclusion principle.
Answer: No two electrons in an atom can have the same set of four quantum numbers; an orbital holds at most two electrons with opposite spins.
Explanation
Explains the maximum of 2 electrons per orbital.
State the Aufbau principle.
Answer: Electrons fill the lowest-energy orbitals first.
Explanation
Order: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p...
How many electrons can the s, p, d, and f sublevels hold?
Answer: s: 2, p: 6, d: 10, f: 14.
Explanation
Each orbital holds a maximum of 2 electrons with opposite spins.
What is an orbital?
Answer: A region of space where there is a high probability of finding an electron.
Explanation
s orbitals are spherical; p orbitals are dumbbell-shaped.
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