Chapter 3 - Atomic and Molecular Structure

All matter is composed of what?

Atoms

What is Dalton’s Atomic Theory?

1. All matter is composed of atoms (indivisible)

2. Atoms of a specific element are identical in mass and properties

3. Compounds are formed by whole number ratios of two or more different atoms

4. A chemical reaction is a rearrangment of atoms

How are compounds formed?

Compounds are formed by whole number ratios of two or more atoms

What is the term for the fundamental unit of matter?

Atom

What is a chemical reaction a rearrangement of?

A rearrangement of atoms

The nucleus is known as?

the inner core of an atom

What are protons?

Protons are positively charged subatomic particles. Carry a charge of +1e and have mass of 1 atomic mass unit (amu)

What are electrons?

Electrons are negatively charged subatomic particles that orbit the nucleus and are involved in chemical bonding. Carry a charge of -1e and have mass of approximately 1/1836 amu.

How can the mass number of an atom be calculated?

Mass number = (# of protons) + (# of neutrons)

What are neutrons?

Neutrons carry no charge and are found in the nucleus of an atom. They ensure the atom’s stability and have a mass of 1 amu

What would happen without neutrons?

the protons would repel each other and make the nucleus unstable.

Are protons heavier or lighter than electrons?

Protons are heavier

Are neutrons heavier or lighter than protons?

Neutrons are heavier ever slightly

What is an neutral atom?

A neutral atom is an atom where the number of protons equals the number of electrons, resulting in no overall electric charge.

What are core electrons?

Core electrons are the inner electrons in an atom that are not involved in bonding and are typically closer to the nucleus. They tend to be most stable and lowest in energy.

What are valence electrons?

Valence electrons are the outermost electrons in the highest energy level of an atom. They have higher energy than core electrons and do not feel the attractive forces of the nucleus and are loosely held. They determine the atom's reactivity and the formation of chemical compounds.

Why are bonds formed with valence electrons?

Bonds are formed with valence electrons because they are more reactive. They form to achieve a more stable electron configuration by having a full valence shell.

Which two subatomic particles make up most of the atom's mass?

Protons and neutrons

What does atomic number (Z) refer to?

Number of protons found in the atom of that specific element

What is the atomic number (Z) useful for?

It acts as a tool for identifying the identity of an unknown element, as this number remains constant across all isotopes of an element (e.g. all carbon atoms have 6 protons)

What does atomic mass (A) refer to?

The weighted average of an element based on its isotopes

What are cations?

Atoms that have lost one or more electrons to become positively charged. Has more protons than electrons.

What are anions?

Atoms that have gained one or more electrons to become negatively charged. Has more electrons than protons.

What is an isotope?

An isotope is an atom of the same element that has a different number of neutrons and the same number of protons, resulting in a different atomic mass.

Do valence electrons have higher or lower energy compared to electrons closer to the nucleus?

Higher energy

What is an element?

An element is a pure substance composed of 1 type of atom. Elements cannot be broken down into simpler substances through physical or chemical reactions and are represented on the periodic table.

What is a compound?

A compound is a substance formed when two or more atoms from different elements chemically bond together (combine). Resulting in unique properties distinct from the individual elements.

What is the law of constant composition?

The law of constant composition states that elements within a chemical compound always combines in a fixed proportion.

What is a physical reaction?

A physical reaction is a process that involves a change in the physical properties of a substance without altering its chemical composition, such as changes in state or appearance. It undergoes a rearrangement to produce a physical change.

A physical reaction can cause a substance to…

more or less dense, change state or appearance.

A physical reaction does not…

create new substances and doesn’t form or destroy new chemical bonds

What is a chemical reaction?

A chemical reaction is a process that involves the transformation of one or more substances into different substances through the breaking and forming of chemical bonds, resulting in new products.

What happens in a chemical reaction?

Intramolecular bonds between atoms are created or destroyed.

What are the five types of chemical reactions?

1. Synthesis

2. Decomposition

3. Single Displacement

4. Double Displacement

5. Combustion

What is a synthesis reaction?

when two or more atoms or molecules combine to form a single compound, A + B = AB. Involves release of energy.

What is a decomposition reaction?

when a compound breaks down into two or more products, AB = A + B. Requires input of energy.

What is a single displacement reaction?

when one element is replaced by another in a compound, AB + C = AC + B.

What is a double displacement reaction?

when two compounds exchange bonds to form two new compounds, AB + CD = AC + BD. Also called exchange reactions, common types are neutralization and precipitation reactions.

What is a combustion reaction?

when a substance reacts with O2 gas to produce light and heat. Typically involves hydrogen, hydrocarbons and oxygen, resulting in carbon dioxide and water as products.

The modern quantum theory has replaced which outdated model?

The Bohr model (described electrons as following defined circular orbits around nucleus)

How does the modern quantum theory describe the pathway of electrons?

Electrons occupy in a 'cloud of electrons' surrounding the nucleus

What does the Heisenberg uncertainty principle describe?

It is impossible to perfectly find both the momentum and the location of an electron in an atom at a given time. In other words, you can figure out one or the other but not both

What does principle quantum number (n) refer to?

Represents the main energy level occupied by electrons

What are the possible values for principle quantum number (n)?

Must be positive integer number, equal or greater than 1

The maximum number of electrons that an electron shell can hold is given by what formula?

2n²

What does azimuthal quantum number refer to (l)?

Describes the shape of the subshells or the orbital shape within each principle energy level

What are the possible values for azimuthal quantum number (l)?

Between zero and the value of the principle quantum number minus 1 (n-1)

If a principle quantum number (n) is 1, what are the potential azimuthal quantum numbers (l)?

Only 0

If a principle quantum number (n) is 4, what are the potential azimuthal quantum numbers (l)?

0, 1, 2, and 3.

What azimuthal quantum number (l) is associated with a 's' subshell?

l = 0

What azimuthal quantum number (l) is associated with the 'p' subshell?

l = 1

What azimuthal quantum number (l) is associated with the 'd' subshell?

l = 2

What azimuthal quantum number (l) is associated with the 'f' subshell?

l = 3

How many electrons can be held in the 's' subshell?

2

How many electrons can be held in the 'p' subshell?

6

How many electrons can be held in the 'd' subshell?

10

How many electrons can be held in the 'f' subshell?

14

What does the magnetic quantum number (ml) refer to?

Describes the orientation of orbitals in space

What are the possible values for magnetic quantum number (ml)?

Number ranges between the negative and positive magnitude of the azimuthal number (l)

What magnetic quantum numbers (ml) are possible for a 'p' subshell?

ml = -1, 0, and 1

What magnetic quantum numbers (ml) are possible for a 'f' subshell?

ml = -3, -2, -1, 0, 1, 2, 3

What does the spin quantum number (ms) refer to?

Describes the angular momentum of an electron. Electrons in the same orbital must have opposite spins.

What are the possible values for spin quantum number (ms)?

ms = +1/2 or -1/2 representing an upward or downward spin.

What does the Pauli exclusion principle state?

No two electrons in an atom can have the exact set of four quantum numbers

What is electron configuration?

The distribution of electrons in an atom's orbitals, following the principles of Aufbau, Pauli exclusion, and Hund's rule. It tells us the number of electrons in each energy level and the order which subshells of an atom are filled.

What is the notation of electron configuration?

1st number indicates the energy level, the letter represents the subshell type, and the superscript shows the number of electrons in that subshell.

ex: 2p6

How many orbitals can you have in each subshell?

s-subshell = 1 orbital

p-subshell = 3 orbitals

d-subshell = 5 orbitals

f-subshell = 7 orbitals.

What is noble gas configuration?

A shorthand notation for electron configuration that uses the nearest noble gas preceding the element to represent inner shell electrons, simplifying the electronic structure.

What does Hund's rule state?

Within a given subshell, orbitals are filled such that the maximum number of half-filled orbitals are obtained. This is why you often see half filled 4s orbitals and half filled 3d orbitals

What does the Aufbau principle state?

Electrons will first occupy lower-energy orbitals before filling higher-energy orbitals

What are the exceptions to electron configuration?

Atoms might borrow an electron from an adjacent subshell to achieve a more stable configuration. Subshells like to be full or half-full.

Now both s & d subshells are half-filled. Ex: Cr & Mo

Now s-subshell is half-filled and d-subshell is completely full. Ex: Cu, Au, Ag

What is an isoelectronic species?

An isoelectronic species are atoms, ions, or molecules that have the same number of electrons, resulting in similar electron configurations. Examples include O2-, F-, and Ne, which all have 10 electrons.

Are covalent bonds weaker or stronger than ionic bonds?

Weaker

Are covalent compounds more likely to have higher melting and pointing points compared to ionic compounds?

No, covalent compounds are more likely to have lower melting and boiling points due to weak covalent bonds

What does bond length refer to?

Distance between nuclei of each atom involved in a bond. Bond shortens as number of shared electrons increases.

What does bond energy refer to?

Energy needed to break a bond between two atoms. Energy increases as number of shared electrons increases.

What does polarity refer to?

The distribution of electrical charge over the atoms in a molecule, determining its partial positive and negative charges. Polarity arises due to differences in electronegativity between atoms.

Does the sharing of electrons in a covalent bond have to be equal?

No. Electrons can be shared unequally in covalent bonds, leading to polarity, typically between non-metals.

A less electronegative atom has?

a partial positive charge in a polar covalent bond, pulls electrons less to its side.

A more electronegative atom has?

a partial negative charge in a polar covalent bond, attracting electrons away to its side.

An equal amount of electronegativities result in?

A nonpolar covalent compound

What are two other types of covalent bonding?

• Covalent network solids: a structure where atoms are connected by covalent bonds in a continuous network. Held together very tightly.

• Coordinate covalent compounds: both electrons involved in the bond come from the same atom.

What is involved in forming ionic bonds?

It involves the complete transfer of electrons from the less electronegative atom to the more electronegative atom. Typically occurring between metals and non-metals.

What are properties of Ionic Compounds?

• Form crystalline structures (hard to break)

• Referred to as Ionic Salts

• Have high melting and boiling points due to strong electrostatic attractions

• Usually soluble in water (dissociate into cations and anions).

• Conduct electricity when melted or dissolved (ions move freely).

What are properties of Covelent Compounds?

• Have lower melting and boiling points

• Exist as liquids or gasses

• Insoluble in water

• Do no conduct electricity in aqueous or molten form

What is involved in forming metallic bonds?

It involves the electrostatic force between the delocalized electrons and positively charged metal ions. The valence electrons are loosely held and become delocalized. Typically between metals.

What are the properties of Metallic Compounds?

• High melting and boiling points

• Conduct electricity due to free-moving electrons

• Malleable can be hammered into sheets

• Ductile can be drawn into thin wires

• Lustrous or shiny

What are the three types of intermolecular forces?

London dispersion force (aka Van der Waals), dipole-dipole, and hydrogen bonds

What is required to form a hydrogen bond?

Hydrogen attached to a very electronegative atom (such as oxygen, nitrogen, or fluorine)

Increasing intermolecular forces results in…

• Increasing melting and boiling points: held more tightly and more energy needed

• Increases viscosity: held more tightly and harder to slide past

• Increases surface tension: more energy required to overcome cohesive forces

• Decreases vapor pressure: less molecules escaping into the vapor phase

What type of bond results from parallel overlap of orbitals?

Pi bond

What type of bond results from head-to-head overlap of orbitals?

Sigma bond

Which bonds are involved in a double bond?

One sigma bond and one pi bond

Which bonds are involved in a triple bond?

One sigma bond and two pi bonds

Between sigma and pi bond, which allows for free rotation at the axis?

Sigma allows free rotation at axis while pi bond does not

What is the bond order of a single bond?

One

What is the bond order of a triple bond?

Three

As the bond order increases, what happens to bond length and bond strength?

Length decreases and strength increases

Does bond strength increase or decrease going down a column on the periodic table?

Decrease. As atomic radii increases, bond length increases resulting in decreased bond strength

How many orbital(s) fill the s-subshell?

1 orbital with a spherical shape that can hold a maximum of 2 electrons.