Unit 1 - Atomic Structures and Properties

First unit of AP Chemistry! Make sure to answer in the definition part, not the term!!!

What is Molar Mass?

What is Molar Mass?

The mass of one mole of a substance, as listed on the periodic table in a unit of grams/mol (g/mol).

What is Avogadro’s number and what does it represent?

6.022 × 10²³ | Represents 1 mol of atoms, particles, etc,.

Conversions can only happen between _____ and _____

moles and “countable” entities (like grams).

NOTICE: There is no direct conversation between “entities” and grams.

What are Mass Spectrometers?

They ionize samples, which are then accelerated and deflected in a vacuum tube until they hit a defector (four main processes).

What are the four main processes in Mass Spectrometers? (name in order)

Ionize Sample, Accelerate it, Deflect it, and Defect it.

What happens to more massive particles in a Mass Spectrometer?

They get deflected less compared to smaller particles because these larger particles have a greater mass and therefore have a greater mass to charge ratio.

What is the end result of spectrometers?

They typically create ions with a +1 charge, however, they can create ions with different charges, hence the mass/charge ratio.

What does the x and y axis show on a mass spectrometer graph?

X-Axis: Shows the mass/charge ratio of ions

Y-Axis: Shows the % abundance of ions (out of 100). It shows this sometimes in relative frequency, where 100 is the most frequent and lower numbers are less frequent.

What happens in Fragmentation of diatomic samples?

These diatomics can result in more lines on the mass spectrum graph.

What is the law of definite proportions? What is it represented by?

It is the ratio of compounds in any pure sample. This ratio will always be the same.

EX: for H₂O, there will always be two H’s for every O.

What is the percent composition of Na in NaCl?

39.3%

Math: 23 (amu of Na)/ (23+35.5) = 0.393

What can a Pure Substance be?

An element (same element together like individual atoms, molecules, or crystals.

OR

A compound (different elements together: molecules, crystals)

What are crystals like in elements? What about in compounds?

Elements
Metallic bond bonded together by one element

Compound
Repeated patterns of multiple different elements

What is the difference between a pure substance and a mixture?

In mixtures, the proportions can vary (like the concentration of Kool Aid) and can only be determined by mass percent (not %-comp).

Pure substances are always the same in elements/compounds. Their proportions will never change.

What are shells?

Energy levels that determine how far away electrons are from the nucleus.

What are subshells?

The types of shells of eletrons (s,p,d,f).

What are orbitals?

Where electrons move randomly within predictable waves. S has one orbital, p has 3, d has 5, and f has 7.

What is the Aufbau Principle?

Electrons fill the lowest energy level first (s, then p, then d, etc) with exceptions at the “d” block.

What is Hund’s Principle?

Electrons fill with arrows going in the same direction before going in opposite directions.

Why is it that if you end with 3d⁴/3d⁹ that you need to pull an electron out of the 4s² sublevel?

It is because it takes less energy.

What is Coulomb’s Law?

It relates the force between two charged particles (not just electrons). It says that it would be easier to rip an electron away the farther it is from the nucleus.

What is Coulomb’s equation?

F_coulombic (fish) q₁*q₂/r²

Where q is the charge of either particle and r is the radius from the nucleus.

What is photoelectron spectroscopy?

It is a machine that shoots energy at an atom. The energy makes electrons fall off.

What happens when you have a low amount of energy from photoelectron spectroscopy?

Only electrons farther away from the nucleus will fall off.

What do the peaks in the graphs (of photoelectron spectroscopy) represent?

The number of electrons that can be removed (or is removed).

Why is it that different elements always have a different PES (photoelectron spectrum)?

Because they all have differently charged nuclei.

Don’t ever use the trend to explain ____ something happened.

why

Instead of using a trend to explain a “why,” what should you use? Give an example!

Coulomb’s law!!!

The trends are a result of Coulomb’s law & the shell model of the atom, and effective nuclear charge.

What happens, according to Coulomb’s law, when you go left to right on the periodic table?

It has the largest effect to q. It will increase drastically because the amount of protons in the nucleus increases.

What happens, according to Coulomb’s law, when you go down groups on the periodic table?

It has the largest effect to r because you have more shells (the radius will increase)!

What happens to the atomic radius as you go across periods, why? What about down families, why?

Across Periods - Decrease
According to Coulomb’s law, there are more protons to attract the electrons, making them closer to the nucleus.

Down families - Increase
According to Coulomb’s law, the inner electrons repel the outer electrons (valence electrons).

What happens to the ionization energy as you go across periods, why? What about down families, why?

Across Periods - Increase
According to Coulomb’s law, there are more protons to attract the electrons from other atoms, which takes more energy.

Down families - Decrease
According to Coulomb’s law, the valence electrons are further from the nucleus, making it easier to rip away an electron.

What happens to the electronegativity as you go across periods, why? What about down families, why?

Across Periods - Increase
According to Coulomb’s law, the amount of protons increase (q) and the atomic radius decreases (r). This makes the tendency to attract additional electrons increase.

Down families - Decrease
According to Coulomb’s law, the combination of increased distance and electron shielding leads to a decrease in electronegativity. There are more electron shells added and an interference with the inner electrons.

What happens to electron affinity as you go across periods, why? What about down families, why?

Across Periods - Increase
According to Coulomb’s law, the number of protons in the nucleus increases, meaning there is a higher q₁. The atomic radius also decreases, making the distance between the nucleus and an electron decrease (r). This makes electron affinity more negative to a neutral atom.

Down families - Decrease
According to Coulomb’s law, there is increased distance between the valence electrons and the nucleus, which increases r. There is also more electron shielding, making it difficult to hold onto electrons. Therefore, the electron affinity would be less negative beause these factors reduce the nucleus’s ability to attract and hol donto an incoming electron.

What happens to the ionic radius as you go across periods, why? What about down families, why?

Across Periods - Decrease
According to Coulomb’s law, as you move across periods, electrons fall off and form cations (like Na⁺). This loss pulls remaining electrons closer to the nucleus and decreases the ionic radius.

According to Coulomb’s law, as you move across periods, atoms will gain electrons (anions), which at first increases the ionic radius, but as you continue, the higher nuclear charge (more protons) pulls electrons closer together.

Down families - Increases
According to Coulomb’s law, ions have more electron shells, increasing the distance (r) between nucleus and outermost electrons, allowing the ionic radius to increase. The shielding effect also allows for a larger ionic radius.

What is the atomic radius?

The distance from the nucleus of an atom to the outermost energy level electrons.

What is ionization energy?

The amount of energy needed to remove an electron from an atom.

What is electronegativity?

The tendency of an atom to attract electrons to itself from a shared bond (can only pull on covalent bonds).

What is electron affinity?

The energy change of a neutral atom when an eletron is added to the atom. High values=easy to gain.

Basically how good an atom is at attracting electrons.

What is ionic radius?

The distance from the nucleus of an ion to the outermost energy level electrons.

What do interactions between valence electrons and nuclei of elements determine (in terms of ionic compounds)?

The likelihood that two elements will form a chemical bond.

When do analogous elements tend to form?

When elements are in the same period of the periodic table.

Why is 2nd ionization energy harder to take away electrons than 1st ionization energy?

It is because when you take an electron away, the ion becomes more positively charged, making it really difficult to remove another electron.