General Chemistry 1 Module 2: Atoms, Isotopes, Ions, Molecules, and Electronic Structure

A comprehensive set of flashcards covering atomic theory, isotopes, ions, periodic table, and electronic structure as presented in the notes.

What are the four postulates of Dalton's Atomic Theory (1808)?

1) Elements are composed of extremely small particles called atoms. 2) All atoms of a given element are identical. 3) Compounds are composed of atoms of more than one element with fixed ratios. 4) Chemical reactions involve rearrangement of atoms; atoms are not created or destroyed.

State the Law of Definite Proportions.

Different samples of the same compound always contain its constituent elements in the same proportion by mass.

State the Law of Multiple Proportions.

If two elements can form more than one compound, the masses of one element that combine with a fixed mass of the other element are in small whole-number ratios.

State the Law of Conservation of Mass.

The total mass before a chemical process equals the total mass after the process.

Name the three subatomic particles and their charges.

Protons (positive), electrons (negative), neutrons (neutral). Protons and neutrons have similar mass; electron mass is negligible.

What is a nuclide?

An atom characterized by its atomic number (Z) and mass number (A).

What does the atomic number Z represent?

The number of protons in the nucleus; for a neutral atom, it equals the number of electrons.

What is mass number A?

Total number of protons and neutrons in the nucleus; A ≈ atomic mass in amu.

How do you find the number of neutrons?

Neutrons = A − Z.

How is a nuclide symbol written?

Z is written as a subscript and A as a superscript to the left of the element symbol, e.g., A/Z X.

What are isotopes?

Atoms of the same element with different masses due to different numbers of neutrons.

What does fractional abundance mean?

The fraction of total atoms that are a particular isotope.

How do you calculate atomic weight?

Sum of (isotopic mass × fractional abundance) for all isotopes of the element.

Define a molecule.

An aggregate of two or more atoms held together by chemical bonds; neutral; may contain the same or different elements.

Name seven diatomic molecules that occur naturally.

H2, N2, O2, F2, Cl2, Br2, I2.

What is a diatomic molecule?

A molecule consisting of two atoms.

Name examples of polyatomic molecules.

H2O, NH3, CH4, O3.

What is an ion?

An atom or group with a net positive or negative charge; electrons may be gained or lost.

What is a cation and what is an anion?

Cation: positively charged ion; Anion: negatively charged ion.

What are monatomic and polyatomic ions?

Monatomic ion: contains a single atom. Polyatomic ion: contains two or more atoms.

Name the groups and their common names: Group IA, IIA, IIIA, IVA, VIA, VIIA, VIIIA.

IA: Alkali metals; IIA: Alkaline earth metals; IIIA: Aluminum/Boron family; IVA: Carbon family; VIA: Chalcogens; VIIA: Halogens; VIIIA: Noble/Inert gases.

What are periods on the periodic table?

Horizontal rows; elements in the same period have the same number of valence shells.

What is the Schrödinger quantum mechanical model of the atom?

A model where electrons are described by probability distributions (electron clouds) rather than exact orbits; introduces orbitals.

What is an orbital?

A three-dimensional space where an electron is most likely to be found (atomic orbitals in atoms; molecular orbitals in molecules).

What are the four quantum numbers and what do they describe?

n (principal, energy level), l (angular momentum, orbital shape), m (magnetic, orbital orientation), s (electron spin).

What does the principal quantum number n designate?

The principal energy level (shell); indicates orbital size; n = 1–7.

What does the angular momentum quantum number l designate?

Orbital shape; l = 0 to n−1; corresponds to s, p, d, f subshells; within a shell, s < p < d < f in energy.

What does the magnetic quantum number m designate?

Orientation of the orbital in space; m values range from −l to +l.

What does the electron spin quantum number s denote?

+1/2 or −1/2; indicates the spin direction of an electron.

What is the Aufbau principle?

Electrons occupy orbitals in order of increasing energy, starting with 1s.

What is the Pauli exclusion principle?

No more than two electrons may occupy the same orbital, and they must have opposite spins.

What is Hund’s rule?

When electrons occupy degenerate orbitals, they enter singly with parallel spins before pairing.

What is the Aufbau mnemonic sequence for filling orbitals (partial listing given in notes)?

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f14 6d10.

What is noble gas shorthand for electron configurations?

Replace filled cores with [Noble gas]; e.g., Cl: [Ne] 3s2 3p5.

What are valence electrons?

Electrons in the outermost energy level; determine bonding capacity; e.g., B has 3 valence electrons (2 in 2s, 1 in 2p).

How are electrons removed or added to form ions with respect to energy levels?

Electrons are removed from the highest energy level to form cations and added to the highest energy level to form anions.

What is an exception to the Aufbau principle and the Cr example?

Sometimes d/f orbitals require extra energy; half-full stability leads to exceptions like Cr: [Ar] 4s1 3d5 instead of [Ar] 4s2 3d4.

What is paramagnetism and when does it occur?

Paramagnetic substances have one or more unpaired electrons and are attracted to magnetic fields.

What is diamagnetism?

Diamagnetic substances have all electrons paired and are weakly repelled by magnetic fields; noble gases are diamagnetic.

What is the Lewis electron dot structure and the octet rule?

LEDS uses dots to denote valence electrons; octet rule states atoms tend to achieve the electron arrangement of the nearest noble gas.

How do you determine valence electrons from an electron configuration?

Count the electrons in the outermost (highest n) energy level; e.g., B has 3 valence electrons (2 in 2s and 1 in 2p).

Provide an example of Ca’s electron configuration and its 4s orbital filling.

Ca: 1s2 2s2 2p6 3s2 3p6 4s2; the 4s orbital is filled with two electrons.

How do you compute the number of neutrons for a nucleus with Z and A?

Neutrons = A − Z.

If a nucleus has Z = 38 and A = 88, how many neutrons are there and what is the isotope symbol?

Neutrons = 88 − 38 = 50; symbol is Sr-88 (Sr with Z=38 and A=88).