Chemistry Review: Atoms, Isotopes, Electrons, and Bonding

A set of practice flashcards covering key concepts from the lecture notes on atomic structure, isotopes, electron configurations, bonding, and molecular structure.

What defines a specific element in an atom (the key defining number)?

The number of protons, i.e., the atomic number.

What is the mass of a proton or neutron (in amu) and why is electron mass often ignored?

Proton and neutron mass ≈ 1 amu each; electron mass is negligible compared to protons/neutrons.

How do you calculate the atomic mass (mass number) of an atom?

Mass number = protons + neutrons.

What is an isotope?

Atoms of the same element (same number of protons) with different numbers of neutrons.

How are isotopes named?

Element name followed by the mass number, e.g., Carbon-12, Hydrogen-3.

Why is the atomic weight on the periodic table a decimal number like 12.01?

It is a weighted average of all isotopes based on their natural abundance.

Which two features mainly determine an atom’s chemical behavior?

The number of electrons and how they are distributed (valence electrons).

From a mass and atomic number, what numbers can you immediately determine for a neutral atom?

Protons from the atomic number; neutrons from mass − protons; electrons equal protons.

What is a shell in an electron diagram and what are the typical capacities of the first three shells?

Shells are electron energy levels; capacities: 1st = 2, 2nd = 8, 3rd = 8 (for early elements).

What is the shell-filling rule?

Fill the inner shell to capacity first, then move to the next shell when the previous is full.

What is an orbital and how many electrons can an orbital contain?

An orbital is a box on a shell where electrons reside; each orbital holds up to 2 electrons.

What is the distribution rule for electrons within a shell?

Within a shell, place one electron in each orbital before pairing two electrons in the same orbital.

What are valence electrons and why are they important?

Electrons in the outermost occupied shell; they largely determine chemical reactivity and bonding.

What is an ionic bond?

A bond formed by transfer of electrons from one atom to another, creating oppositely charged ions that attract.

How is an ionic charge calculated?

Ionic charge = protons − electrons (positive if electrons are lost, negative if gained).

In NaCl, what happens to sodium and chlorine to form ions?

Sodium loses 1 electron to become Na+; chlorine gains 1 electron to become Cl−.

Do ions in an ionic compound have full valence shells?

Yes; ions tend to have full outer shells when the bond forms.

Do salts have discrete molecules?

No; salts are ionic compounds and do not consist of discrete molecules.

What is a covalent bond?

A bond formed by sharing of electrons between atoms, allowing both to effectively gain electrons.

In CH4 (methane), how many covalent bonds does carbon form and why?

Four covalent bonds; carbon needs four more electrons to complete its valence shell.

How many covalent bonds do nitrogen, oxygen, and hydrogen typically form?

Nitrogen usually forms 3; oxygen 2; hydrogen 1 covalent bonds.

What is a carbon skeleton?

A central carbon framework (backbone) around which a molecule is built.

What is a molecule versus a compound?

A molecule is atoms held together by covalent bonds; a compound is a substance made of two or more elements (can be ionic, e.g., salts).

Which four elements make up most biological molecules (the big four)?

Oxygen, carbon, hydrogen, and nitrogen.

What order should you follow when building a molecule from a formula (C, N, O, H) and why?

Start with carbons to form a carbon skeleton, then add nitrogens, then oxygens, then hydrogens; this follows the most-bonds-to-fewest rule.

How many bonds does carbon typically form and why?

Four bonds, to reach a full valence shell of eight electrons.

What is polar covalent bonding and what causes it?

Unequal sharing of electrons in a covalent bond due to differences in electronegativity (e.g., oxygen pulls electrons more).

Which element tends to win tug-of-war over shared electrons, making bonds polar?

Oxygen, which is highly electronegative, often garners the shared electrons more, creating partial negative charge on oxygen.