Chemistry

What determines the identity of an element?

Number of protons.

What is atomic number?

Number of protons.

What is mass number?

Protons plus neutrons.

What are isotopes?

Atoms of the same element with different numbers of neutrons.

What changes when an atom becomes an ion?

Number of electrons.

What is a cation?

Positive ion formed by losing electrons.

What is an anion?

Negative ion formed by gaining electrons.

What are valence electrons?

Outer-shell electrons involved in bonding.

What is Coulombic attraction?

Opposite charges attract. Attraction is stronger with larger charges and smaller distance.

What happens to Coulombic attraction when distance increases?

Attraction decreases.

What happens to Coulombic attraction when charge magnitude increases?

Attraction increases.

What is effective nuclear charge?

The net positive pull felt by valence electrons.

What is shielding?

Inner electrons block valence electrons from feeling the full nuclear charge.

What is the atomic radius trend?

Atomic radius increases down and left.

Why does atomic radius increase down a group?

Atoms gain energy levels and shielding increases.

Why does atomic radius decrease across a period?

Effective nuclear charge increases and pulls electrons closer.

What is the ionization energy trend?

Ionization energy increases up and right.

What is ionization energy?

Energy required to remove an electron from a gaseous atom or ion.

Why does ionization energy increase across a period?

Stronger nuclear attraction holds electrons more tightly.

Why does ionization energy decrease down a group?

Electrons are farther from the nucleus and more shielded.

What is the electronegativity trend?

Electronegativity increases up and right excluding noble gases.

What is electronegativity?

Ability of an atom in a bond to attract electrons.

What are metals usually like?

They tend to lose electrons and form cations.

What are nonmetals usually like?

They tend to gain or share electrons.

What are metalloids?

Elements with properties between metals and nonmetals.

What charge do Group 1 elements usually form?

+1.

What charge do Group 2 elements usually form?

+2.

What charge do Group 17 elements usually form?

-1.

What charge do Group 16 elements usually form?

-2.

What is an atomic orbital?

A region of high probability for finding an electron.

Maximum electrons in one orbital?

2.

Maximum electrons in an s subshell?

2.

Maximum electrons in a p subshell?

6.

Maximum electrons in a d subshell?

10.

Maximum electrons in an f subshell?

14.

What is the Aufbau principle?

Electrons fill lower-energy orbitals first.

What is the Pauli exclusion principle?

Two electrons in the same orbital must have opposite spins.

What is Hund's rule?

Electrons occupy equal-energy orbitals singly before pairing.

What is the orbital filling order through 4p?

1s 2s 2p 3s 3p 4s 3d 4p.

What are core electrons?

Inner electrons not in the valence shell.

What are valence electrons for main-group elements?

Electrons in the highest principal energy level.

What does PES measure?

Electron binding energies.

In PES what does peak position show?

Binding energy.

In PES what does peak area show?

Relative number of electrons.

What does higher PES binding energy mean?

The electron is held more tightly.

Which electrons have higher PES binding energy?

Core electrons.

What is average atomic mass?

Weighted average of isotope masses.

How do you calculate average atomic mass?

Multiply each isotope mass by fractional abundance and add.

What is a mole?

6.022 x 10^23 particles.

What is Avogadro's number?

6.022 x 10^23.

How do you find moles from mass?

moles = grams / molar mass.

How do you find mass from moles?

grams = moles x molar mass.

What is percent composition?

mass of element in compound / molar mass of compound x 100.

What is an empirical formula?

Simplest whole-number ratio of atoms.

What is a molecular formula?

Actual number of atoms in a molecule.

How do you get molecular formula from empirical formula?

Divide molecular molar mass by empirical formula mass to find the multiplier.

What is an ionic bond?

Electrostatic attraction between oppositely charged ions.

Ionic bonds usually form between what?

A metal and a nonmetal.

What is a covalent bond?

Sharing of electrons between nonmetals.

What is a metallic bond?

Attraction between metal cations and delocalized electrons.

What is a polar covalent bond?

Unequal sharing of electrons.

What is a nonpolar covalent bond?

Equal or nearly equal sharing of electrons.

What does a larger electronegativity difference mean?

A more polar bond.

In a polar bond electrons are pulled toward what atom?

The more electronegative atom.

What is the most electronegative element?

Fluorine.

What highly electronegative atoms should you remember?

F O N Cl.

What increases lattice energy?

Larger ion charges and smaller ion sizes.

What usually happens when lattice energy is higher?

Melting point is higher and the ionic solid is harder.

What is the purpose of a Lewis structure?

To show valence electrons and bonding.

First step for drawing a Lewis structure?

Count total valence electrons.

What atom usually goes in the center of a Lewis structure?

The least electronegative atom except hydrogen.

What is the octet rule?

Many atoms are stable with 8 valence electrons.

What is the duet rule?

Hydrogen is stable with 2 electrons.

How many electrons are in a single bond?

2.

How many electrons are in a double bond?

4.

How many electrons are in a triple bond?

6.

What is the formal charge formula?

formal charge = valence electrons - nonbonding electrons - 1/2 bonding electrons.

What makes a good Lewis structure?

Small formal charges and negative charge on more electronegative atoms.

What is resonance?

Multiple valid Lewis structures that differ only in electron placement.

What does resonance imply?

Electrons are delocalized.

What happens to bond length as bond order increases?

Bond length decreases.

What happens to bond strength as bond order increases?

Bond strength increases.

What is the single double triple bond length order?

Single longest. Double shorter. Triple shortest.

What is the single double triple bond strength order?

Single weakest. Double stronger. Triple strongest.

What is VSEPR theory?

Electron groups repel and arrange to minimize repulsion.

Electron geometry with 2 electron groups?

Linear.

Electron geometry with 3 electron groups?

Trigonal planar.

Electron geometry with 4 electron groups?

Tetrahedral.

Molecular shape with 2 groups and 0 lone pairs?

Linear.

Molecular shape with 3 groups and 0 lone pairs?

Trigonal planar.

Molecular shape with 4 groups and 0 lone pairs?

Tetrahedral.

Molecular shape with 4 groups and 1 lone pair?

Trigonal pyramidal.

Molecular shape with 4 groups and 2 lone pairs?

Bent.

Linear bond angle?

180 degrees.

Trigonal planar bond angle?

120 degrees.

Tetrahedral bond angle?

109.5 degrees.

Trigonal pyramidal bond angle?

Slightly less than 109.5 degrees.

Bent bond angle with 4 electron groups?

Less than 109.5 degrees.

What do lone pairs do to bond angles?

They compress or decrease bond angles.

What determines molecular polarity?

Bond polarity and molecular shape.