General Chemistry

108 flashcards by MentisLibrary

First-year chemistry from atoms to electrochemistry: atomic structure and periodic trends, bonding and molecular shape, stoichiometry, gases, solutions, thermochemistry, kinetics and equilibrium, acids and bases, and redox.

Give the charge and relative mass of the proton, neutron and electron.
Proton: charge +1, mass about 1 atomic mass unit. Neutron: charge 0, mass about 1 amu. Electron: charge -1, mass about 1/1836 of a proton.
What do the atomic number and the mass number tell you?
The atomic number is the proton count and defines the element. The mass number is protons plus neutrons in one particular atom.
What are isotopes and how is average atomic mass calculated?
Atoms of one element with different neutron counts. The tabulated atomic mass is the sum of each isotope's mass times its fractional abundance.
How do cations and anions form, and how does size change?
A cation forms when an atom loses electrons and it becomes smaller than the parent atom. An anion forms when an atom gains electrons and it becomes larger.
Why did the Bohr model have to be replaced?
It fixed electrons in circular orbits of definite radius, which predicts hydrogen's spectrum but fails for every atom with more than one electron.
Name the four orbital types and how many electrons each sublevel holds.
s holds 2 electrons in 1 orbital, p holds 6 in 3 orbitals, d holds 10 in 5 orbitals, f holds 14 in 7 orbitals.
State the Aufbau principle, the Pauli exclusion principle and Hund's rule.
Aufbau: electrons fill the lowest available energy first. Pauli: no two electrons in one atom share all four quantum numbers, so an orbital holds at most two with opposite spins. Hund: within equal-energy orbitals, electrons occupy them singly with parallel spins before pairing.
Write the electron configuration of sulfur in full and in noble gas shorthand.
Full: 1s2 2s2 2p6 3s2 3p4. Shorthand: [Ne] 3s2 3p4.
Why are chromium and copper exceptions to the expected filling order?
A half-filled or completely filled d sublevel is unusually stable, so one 4s electron shifts into 3d. Chromium is [Ar] 3d5 4s1 and copper is [Ar] 3d10 4s1.
What are valence electrons and how do you find the count for a main-group element?
The electrons in the outermost energy level, which are the ones involved in bonding. For a main-group element the count equals the group number's last digit.
Relate a photon's energy to its frequency and wavelength.
Energy rises with frequency and falls with wavelength.
Why does a heated element emit a line spectrum instead of a continuous one?
Electrons can only occupy discrete energy levels, so a falling electron emits a photon of one specific energy, producing sharp lines rather than a smooth band.
What is effective nuclear charge and how does shielding affect it?
The net positive charge an outer electron actually feels, after inner electrons screen part of the nuclear charge.
What is the difference between a period and a group on the periodic table?
A period is a horizontal row and corresponds to the highest occupied energy level. A group is a vertical column and collects elements with the same valence electron arrangement.
Name the alkali metals, alkaline earth metals, halogens and noble gases and give the ion each forms.
Alkali metals are group 1 and form +1 ions. Alkaline earth metals are group 2 and form +2 ions. Halogens are group 17 and form -1 ions. Noble gases are group 18 and normally form no ions.
How does atomic radius vary across a period and down a group?
It decreases left to right across a period as effective nuclear charge pulls the same shell tighter, and increases down a group as new shells are added.
How does ionization energy vary across the table and why?
It increases left to right and decreases down a group. Higher effective nuclear charge and smaller radius hold electrons more tightly; more shells hold them more loosely.
Why is there a large jump between successive ionization energies?
Once the valence shell is emptied, the next electron must come from a core shell much closer to the nucleus, which costs far more energy.
How does electronegativity vary and what scale is used?
It increases up and to the right, excluding the noble gases. On the Pauling scale, fluorine is highest at 3.98 and the group 1 metals are lowest.
How do metallic and nonmetallic character vary?
Metallic character increases down a group and to the left. Nonmetallic character increases up and to the right.
What is an isoelectronic series and how do the radii compare?
Ions and atoms with the same electron count. Within the series, radius decreases as nuclear charge rises, because the same electrons are pulled by more protons.
What is an ionic bond and what properties follow from it?
Electrostatic attraction between oppositely charged ions formed by electron transfer, usually metal to nonmetal. Ionic compounds have high melting points, are brittle, and conduct electricity when molten or dissolved but not as solids.
What is a covalent bond and how do covalent properties differ from ionic?
Sharing of electron pairs between nonmetals. Molecular covalent substances have low melting and boiling points, are often gases or liquids, and do not conduct electricity.
What is metallic bonding?
Metal cations in a lattice sharing a delocalized sea of mobile valence electrons.
How does the electronegativity difference classify a bond?
Roughly, a difference under 0.4 is nonpolar covalent, 0.4 to about 1.7 is polar covalent, and above about 1.7 is ionic.
What is the octet rule and which common cases break it?
Atoms tend to gain, lose or share electrons to reach eight valence electrons. Exceptions: hydrogen and helium want two, boron and beryllium are stable with fewer, elements from period 3 down can expand past eight, and odd-electron species such as NO cannot pair fully.
How do you calculate formal charge and what is it for?
Formal charge equals valence electrons minus lone-pair electrons minus half the bonding electrons. The best Lewis structure minimizes formal charges and puts any negative one on the most electronegative atom.
What is resonance and what does the real molecule look like?
When more than one valid Lewis structure can be drawn, the actual molecule is a single average of them, not a mixture and not a rapid interconversion.
Use VSEPR to give the shape for 2, 3 and 4 electron domains with no lone pairs.
Two domains give linear at 180 degrees. Three give trigonal planar at 120 degrees. Four give tetrahedral at 109.5 degrees.
How do lone pairs change the shape and the bond angle?
Lone pairs occupy a domain but are not seen in the shape name, and they push harder than bonding pairs, compressing the remaining angles.