Chapter 3: Atoms, Elements, and the Building Blocks of Matter

Question 1

2 and 3

Answer 1

2: atomic number, number of protons, also same as the number of electrons surrounding the nucleus of an element in its neutral state.
3: The molar mass of the element. It’s also called the atomic weight

Question 2

Mass number and isotopes

Answer 2

Mass number: sum of neutros and protons

Isotope: different numbers of neutrons. Example - carbon-12 contains 6 protons and 6 neturons, and carbon-14 contains 6 protons and 8 neutrons. These are isotopes of carbon

Molar mass on periodic table - average of all the mass numbers of all known isotopes

Question 3

What are the horizontal and vertical rows called on the periodic table?

Answer 3

Periods: horizontal rows

Groups: verticle columns

Question 4

What do the coefficients in chemical reactions tell you?

Answer 4

About the reactants and products in terms of moles

Question 5

Avagadro’s number

Answer 5

1 mole = 6.022 x 10²³ molecules

Moles = Molecules/(6.022 x 10²³)

Question 6

What are the atomic weights on the periodic table?

Answer 6

They are given in terms of atomic mass units (amu), but an amu is the same as a gram per mole, so if 1 carbon weighs 12 amu, then 1 mol of carbon atoms weighs 12 grams.

Question 7

Equation to convert between grams & moles

Answer 7

Moles = grams/molar mass

Question 8

What is the ideal gas equation?

Answer 8

PV = nRT

P = pressure

V = Volume (L)

T = Temperature (K)

R = the gas constant, 0.0821 L-atm/mol-K

Question 9

What is STP?

Answer 9

Where P = 1 atm

T = 273

And, in this situation, one mole of gas always occupies 22.4 L

So Moles = liters/(22.4 L/mol)

Question 10

Other ways for finding Moles =

Answer 10

(molarity)(liters of solution)

(molality)(kilograms of solvent)

Question 11

What is percent composition (or mass percent)?

Answer 11

Percent by mass of each element that makes up a compound

Calculated by dividing the mass of each element or component in a compound / by the total molar mass for the substance (x 100%)

Question 12

Emperical Formula

Molecular Formula

Answer 12

Represents the simplest ration of one element to another in a compound. Example: CH₂O

Represents the actual formula for the substance. Example: C₆H₁₂O₆

Question 13

What are quantum numbers?

Answer 13

Numbers that describe the positions of the electrons in relation to the nucleus

Each electron has 4 ________ that apply to its **shell, subshell, oribtal, **and spin.

Question 14

Shells

Answer 14

n =1, 2, 3…

In a hydrogen atom, the principal quantum number, or shell, of an electron determines its averge distance from the nucleus as well as its energy.

So, electrons in shells with higher values are farther away on average from the nucleus and will have more energy and less stability than electrons in shells with lower values.

Question 15

Subshells

Answer 15

L = 0, 1, 2…

The angular momentum quantum number, or subshell, describes the shape of an electron’s orbital

• First shell (n = 1) has 1 subshell: s, or l = 0 [n - 1]
• Second shell (n = 2) has 2 subshells: s (l = 0) and p (l = 1)
• Third shell (n = 3) has 3 subshells: s (l = 0), p (l = 1), & d (l = 2)

Orbitals of s sbushells are spherical

Oritals of p subshells are dumbbell shaped

Question 16

Orbitals

Answer 16

m_l, = … -1, 0, +1...

The magnetic quantum number, or orbital, describes the orientation of the orbital in space

Describes whether the path of the electron lies mostlhy on the x, y, or z axis of a 3-dimensional grid

• s subshell (l = 0) has 1 orbital: m_l = 0
• p subshell (l = 1) has 3 orbitals: m_l = -1, m_<em>l</em> = 0, m_l = +1
• d subshell (l = 2) has 5 orbitals: m_<em>l</em> = -2, -1, 0, 1, and 2

Question 17

Spin

Answer 17

m_s = +1/2, -1/2

Each orbital can contain 2 electrons: one with a positive spin and one with a negative spin

Question 18

Aufbau Principle

Answer 18

When building up the electron configuration of an atom, electrons are placed in orbitals, subshells, ad shells in order of increasing energy

Question 19

Pauli Exclusion Principle

Answer 19

Within an atom no electron can have the same set off quantum numbers. Each electron in any atom has its own distinct set of 4 quantum numbers

Question 20

Hund’s Rule

Answer 20

When an electron is added to a subshell, it will always occupy an empty oribtal if one is availabe. Electrons always occupy orbitals singly if possible and pairup if no empty orbitals are available

Question 21

Electrons and Energy

Answer 21

Electrons have potential energy that increases with their distance from the nucleus

Energy of electrons is quantized. Means that electrons can exist only at specific energy levels, separated by specific intervals. Ex. - brick in the building could be placed only on 1st, 2nd, or 3rd floor, but not in between

Quantized energy of an electron in an H atom can be found if you know its principal quantum number or shell

Question 22

How do you find the energy of an electron?

Answer 22

E_<em>n</em> = -2.178 x 10^-8/n² Joules

E_<em>n</em>= energy of the electron

_<em>n</em> = principal quantum number of the electron

Question 23

What happens when atoms absorb energy in the form of electromagnetic radiation?

Answer 23

Electrons jump to higher energy levels. When electrons drop from higher to lower energy levels, atoms give off energy in the form of electromagnetic radiation.

Question 24

Relationship between the change in energy level of an electron and the electromagnetic radiation absorbed or emitted

Energy and Electromagnetic Radiation

Answer 24

ΔE = hv = hc/λ

ΔE = energy change

• h *= Planck’s constant, 6.63 x 10^-34 joule-sec
• v* = frequency of the radiation

λ = wavelength of the radiation

c = the speed of light, 3.00 x 10⁸ m/sec (c = λf)

energy level changes for the electrons of a particular atom are always the same, so atoms can be identified by their emission & absorption spectra

Question 25

Dalton’s Elements

Answer 25

John Dalton:

• There are many different kinds of atoms, called elements
• These elements combine to form compounds - always contain the same ratios of elements. Ex. - Water (H₂O) always has 2 hydrogen atoms for every oxygen atom
• Atoms are never created or destroyed in chemical reactions

Question 26

Development of the Periodic Table

Answer 26

Dmitri Mendeleev and Lothar Meyer

Question 27

Thomson’s Experiment

Answer 27

J.J Thomson watched the deflection of charges in a cathode ray tube and said that atoms are composed of positve and negative charges. The negative charges were called electrons sprinkled throughout the positively charged atom like chocolate chips sprinkled through a blob of cookie dough.

Question 28

Millikan’s Experiment

Answer 28

Calculated the charge on an electron by examining the behavior of charged oil drops in an electric field

Question 29

Plum Pudding Model

Answer 29

Question 30

Rutherford’s Experiment

Answer 30

Ernest Rutherford fired alpha particles at gold foil & observed how they were scattered. Led him to conclude that all positive charge in an atom was concentrated at the center and that an atom is mostly empty space. Led to the ide athat an ato has a positively charged nucleus, which contains most of the atom’s mass, and that the tiny negatively charged electrosn travel around the nucleus.

Question 31

Quantum Theory

Answer 31

Max Planck figured out that electromagnetic energy is quantized. That is, for a given frequency of radiation (or light), all possible energies are multiples of a certain unit of energy, called a quantum (mathematically, thats E = hv).

Question 32

Bohr Model

Answer 32

Neils Bohr predicted that electrons orbit the nucleus at specific, fixed radii. Bohr model worked for atoms and ions with one electron but not for more complex atoms.

Question 33

Heisenberg Uncertainty Principle

Answer 33

Werner Heisenberg: impossible to know bot the position and momentum of an electron at a particular instant. An electron orbital is a probability function

Question 34

De Broglie Hypothesis

Answer 34

All matter has wave characeristics. Sometimes the behavior of electrons is better described in terms of waves than particles

Question 35

De Broglie equation

Answer 35

De Broglie’s hypthesis is useful for very small particles, such as electrons. For larger particles, the wavelength becomes too small to be of interest

Question 36

Periodic trends

Answer 36

The closer the electron is ot he nucleus, the more stronger it is attracted

The more protons in a nucleus, the more strongly an electron is attracted

Electrons are repelled by other electrons in an atom. So if other electrons are between a valence electron and the nucleus, the valence electron will be less attracted to the nucleus. That’s called sheilding

Completed shells (and to a lesser extent, completed subshells) are very stable. Atoms prefer to add or subtract valence electrons to create complete shells if possible.

Metallic character of the elements decreases as you move from left to right across the periodic table. The elements in the borderline between metal and nonmental, such as silicon and arsenic, are called metalloids.

Question 37

Atomic Radius

Answer 37

The approximate distance from the nucleus of an atom to its valence electrons

Question 38

Moving from left to right across a period

Answer 38

Atomic radius decreases

(Li - Ne for example)

Moving from left to right, protons are added to the nucleus. Electrons are also being added, but they are all in the same shell at about the same distance from the nucleus, so there is not much of a sheilding effect.

Question 39

Moving Down a Group

Answer 39

(Li to Cs, for instance) Atomic Radius increases

Moving down a group, shells of eectrons are added to the nucleus. Each shell shields the more distant shells from the nucleus and the valence electrons get farther away from the nucleus. Protons are also being added, but the shielding effect of the negatively charged electron shells cancels out the positive charge.

Question 40

Cations

Answer 40

Smaller than atoms

When an electron is removed from an atom, the outer shell is lost, making the cation smaller than the atom. Also, when electrons are removed, electron-electron repulstions are reduced, allowing all of the remaining valence electrons to move close to the nucleus.

Question 41

Anions

Answer 41

Negatively charged Ions

Larger than Atoms

When an electron is added to an atom, forming an anion, electron-electron repulsions increase, causing the valence electrons to move farther apart, which increases the radius

Question 42

Ionization energy

Answer 42

Electrons are attracted to the nucleus of an atom, so it takes enrgy to remove an electron. The energy required to remove an electron from an atom is called the first ionization energy. Once it has been removed, the atom becomes a positively charged ion. The energy required to remove the next electron from the ion is called the second ionization energy, etc.

Question 43

Moving from left to right acrss a period…

Answer 43

Ionization energy increases

Protons are added to the nucleus, which increases its positive charge. for this reason, the valence electrons are more strongly attracted o the nucleus, which increases the energy required to move them. Electrons are also being added, but sheilding effect provided by the filling of the s subshell causes slight deviation in the trend in moving from Group 2A to Group 3A

There is also a slight deviation when the electrons in the p subshell start to pair up, so oxygen has a slightly lower first ionization energy than nitrogen does.

Question 44

Moving Down a Group

Answer 44

Ionization Energy Decreases

Shells of electrons are added to the nucleus

Inner shell shields the more distant shells from the nucleus, reducing the pull of the nucleus on the valence electrons and making them easier to remove

Protons also being added, but sheilding effect cancels

Question 45

Second Ionization Energy

Answer 45

Greater than the First because when an electron has been removed from an atom, electron-electron repulsion decreases and the remaining valence electrons move closer to the nucelus. This increases the attractive force

Question 46

Electron affinity

Answer 46

A measure of the change in energy of an atom when an electron is added to it

When the addition of an electron makes the atom more stable, energy is given off

When the addition of an electron makes the atom less stable, energy must be placed in a higher energy level, making the element less stable.

Question 47

Electronegativity

Answer 47

Refers to how strongly the nucleus of an atom attracts the electrons of other atoms in a bond.

Electronnegativities of elements are estimated based on ionization energies and electron affinities, and they basically follow the same trends.

Moving from left to right across a period, electronegativity increases

Moving down a goup, electronnegativity decreases