UNIT 1 REVIEW QUESTIONS

What is Avogadro's number? What does this number represent in chemistry?

Avogadro's number is 6.002 x 10^23 and is the number of atoms that are in a single mole of an element

How are the number of moles calculated?

The number of moles of an element or compound are found by dividing the mass (g) of the element or compound and dividing it by the molar mass (found on the periodic table) of the element or compound.

How are the moles of gas calculated (include units for each variable)?

The moles of gas are found by dividing the product of pressure (atm) and volume (L) by the product of Temperature (K) and the gas constant (0.821)

What is molarity? How is it calculated?

Molarity is the concentration of a solution in terms of volume. It is found by dividing the moles of solute by the volume (L) of the solution.

What is percent composition? How is it calculated?

Percent composition is the percent by mass of each element in a compound. It is found by dividing the total mass of each element by the total molar mass of the compound.

What is the difference between the empirical and molecular formulas for a compound?

The empirical formula represents the simplest ratio of one element to another in a compound while the molecular formula represents the actual formula for the substance.

How does the potential energy of an electron change the farther it is from the nucleus? What does it mean that the energy of electrons is quantized?

The potential energy of an electron increases as its distance from the nucleus increases. All electrons energies are quantized meaning that they can only exist at a specific energy level and will always return to that energy level.

What is Coulomb's Law? How does a change in charge or distance affect the electrostatic force? What is binding energy and how is it related to the electrostatic force?

Coulomb's law measures the electrostatic force between charges and is measured as (magnitude of charge 1)(magnitude of charge 2)/(distance between charges squared). If the resulting force is positive then there is a repulsive force, but is the force is negative than it is a attractive force. If the magnitude of the charge increases then so will the force; however, even more importantly, if the distance between the charges increases, their attraction decreases, vice versa. Binding energy is the amount of energy required overcome the electrostatic attraction and remove an electron from an atom.

What is the relationship between energy levels and their electrons energy? What happens when an electron absorbs or releases electromagnetic radiation?

The closer an energy level is the nucleus, the less energy its electrons have. When electrons absorb electromagnetic radiation they jump to a higher energy level, when the release electromagnetic radiation, they fall to a lower energy level.

How is ionization energy related to photoelectron spectroscopy?

The higher the ionization energy of an electron, the less kinetic energy it will have after being ejected from an atom (using electromagnetic radiation),. Therefore, the farther an electron is the nucleus, the faster it will be moving and it will land accordingly on the photoelectron spectrum.

How do you predict the ionic charges of atoms on the periodic table?

You can predict the ionic charges of an element on the periodic table by how many valence electrons it has. If the atom has 5 or more valence electrons, it is going to gain electrons to complete its energy level - thus becoming a anion. If the atom has 3 or less valence electrons, it is going to lose electrons to go down to the next complete energy level - thus becoming a cation. The charges the transition metals make, though always a cation, depends on the compound they are in (except zinc is always +2 and silver is always +1)

What three basic rules make up the foundation of periodic trends?

1. Electrons are attracted to the protons in the nucleus of the atom; the closer the electron is to the nucleus, the more strongly it is attracted; the more protons in a nucleus, the more strongly a electron is attracted. 2. Electrons are repelled by other electrons in an atom; thus, if other electrons are between valence electrons and the nucleus, the valence electrons will be less attracted to the nucleus (shielding). 3. Completed shells (and to lesser extent, completed subshells) are very stable; atoms will add or subtract valence electrons to create complete shells if possible.

How does atomic radius change as you move left to right across a period? Why? What about as you move up and down a group? How do Cations and Anions atomic radius differ from a neutral atom?

As you move left to right across a period, the atomic radius decreases because protons are being added to the nucleus which increases the attraction of the valence electrons to the nucleus, decreasing the atomic radius. As you move from the top to the bottom of a group, the atomic radius increases because shells of electrons (an energy level) is being added which increases the valence electrons distance from the nucleus and increases the shielding effect of the core electrons. When electrons are removed to form a cation, the outermost energy level is lost which decreases the radius, further, electron-electron repulsions are reduced allowing remaining valence electrons to move closer to nucleus. When electrons are added to an atom to form an anion, electron-electron repulsions are increased which causes the valence electrons to move further apart and the radius to increase.

How does the first ionization energy change as you move left to right across a period? Why? What about as you move down a group? Why is the second ionization energy greater than the first ionization energy?

As you move left to right across a period, the first ionization energy increases because as protons are being added the attraction of the valence electrons to the nucleus is increasing which makes them harder to remove. As you move down a group, the first ionization energy decreases because shells are being added that increases the distance of the valence electrons from the nucleus and the inner shells are increasing the electron shielding and decreasing the nucleus's pull making the electrons easier to remove. The ionization energy increases every time an electron is removed because electron-electron repulsion decreases and allows the electrons to move closer to the nucleus.

How does the ionization change once a shell is empty? How does it change when the sublevel is half empty? How does it change when the sublevel changes?

The ionization energy increases greatly once a shell is empty because the next shell is closer to the nucleus and is completely full. When a shell is half empty, there is no electron-electron repulsion within the sublevel and it is harder to remove that electron than the next. When a sublevel is completely empty, the next electron is harder to remove because it is in a sublevel that is completely full and closer to the nucleus.

What two factors affect electronegativity? How does it increases as you move left to right across a period? Why? What about as you move down a group? What are the exceptions?

The two factors that affect electronegativity are its size (the smaller an atom's radius, the more effectively its nuclear charge will be felt past its outermost shell), and its valence electrons (the closer it is to having a full energy level, the more likely it is to attract electrons to complete that level). Thus, as you move from left to right, the electronegativity increases because the atomic radius is decreasing which increases the nucleus's pull on other atom's electrons and the outer shell is getting closer to having a complete shell. As you move down a group, the electronegativity decreases because the atomic radius is increasing which decreases the nucleus pull on other atom's electrons. The exceptions to these rules are the noble gases Helium, Neon, and Argon which cannot form bonds and therefore are not electronegative.

What are the atomic four forces?

The four forces that govern how particles and therefore atoms act are gravitational force (does not affect atoms), electromagnetic force (attractive and repulsive forces), strong nuclear force(overcomes repulsive force between protons and holds them together, weakens as distance grows), and weak nuclear force.

What do the peaks on mass spectroscopy represent?

The peaks on a mass spectrum represent the different isotopes of an element and their relative abundance

What are the exceptions to electron configuration?

The elements in group 6 (transition metals starting with chromium) will have only one electron in their outermost s orbital and 5 in their outermost d orbital. In the same way, elements in group 11 will have 1 element in their outermost s orbital and 10 in their d orbital. This is due to orbitals being much more stable in their half-full of full states so the s electron moves to the d orbital to make it more stable.

What are the diatomic elements?

Nitrogen, Hydrogen, Oxygen, Fluorine, Chlorine, Bromine, Iodine

What are the three rules that govern how electrons are ordered in an atom?

Hund's Rule: there must be one electron of the same spin in each orbital before they can begin to pair; Pauli Exclusion Principle: Two electrons that occupy the same orbital must have opposite spins; Aufbau Principle: electrons occupy orbitals in order of increasing energy.

How are the valence electrons in an atom determined?

The valence electrons are the number of electrons in the outermost s and p orbitals of an atom.

What is effective nuclear charge?

The actual force exerted on any electron by the nucleus of an atom. Is equal to the total number of protons - the shielding constant (usually the number of core electrons).

What are the properties of metals?

Shiny luster, conduct heat and electricity, malleable and ductile, solids at room temperature (except mercury), low ionization energies, and form cations. Will react with oxygen to create metal oxides and tend to be basic.

What are the properties of nonmetals?

All forms of mass, dull, brittle, poor conductors, large electron affinities, and form anions. Will react with oxygen to form non-metal oxides which are acids.

What are the major groups in the periodic table? What are their properties?

The Alkali Metals (Group 1 excluding Hydrogen; exist in 1+ state, shiny, soft, and highly reactive; low density; react quickly with air and violently with water), Alkali Earth Metals (Group 2; high melting points that alkali metals, exist in 2+ state, not as reactive as alkali metals), Chalcogens (Group 16; reactive to alkali earth metals, usually exist in 2- state, both nonmetals and metalloids), Halogens (Group 17; highly reactive and toxic, fluorine most reactive of all elements, high electronegativity, form diatomic molecules), and Noble Gases (Group 18; inert, tasteless, odorless, and non-flammable, no electronegativity, low melting and boiling points).

What is the difference between formula weight and molar mass?

While they both have the same value for any given element or compound, formula weight is measured in amus while molar mass in measure in grams/mole.