Atoms

Question 1

If the number of protons is x than the number of electrons, a positively charged ion, or x, is formed.

Answer 1

• greater
• cation

Question 2

If the number of protons is x than the number of electrons, a negatively charged ion, or x, is formed.

Answer 2

• less
• anion

Question 3

element definition

Answer 3

• simplest form of matter that retains its own unique properties, which are different from all other elements.
• The Periodic Table of the Elements lists all of the known elements in the universe.

Question 3

mass vs atomic number

Answer 3

• Ar is number of P
• MN is number of P+N

Question 4

mixture defintion

Answer 4

• Mixtures involve two or more substances that are physically mixed or intermingled.
• However, these substances are not chemically bonded together. Therefore, the substances can be present in any ratio.

Question 5

homogenous mixture def

Answer 5

• has the same composition throughout the entire mixture.
• if you take a sample from any part of the mixture, it will look and be the same.

Examples:
- Salt water: Once the salt dissolves in the water, the mixture looks uniform, and you can’t see or separate the salt from the water by looking at it.

Question 6

heterogeneous mixture def

Answer 6

• has a non-uniform composition, meaning that different parts of the mixture may look or behave differently.
• Examples:
  Salad: Each part of a salad might have different ingredients, like lettuce, tomatoes, cucumbers, etc. The composition changes from one bite to another.

Question 7

Which of the following descriptions is used to describe the liquid state?

Answer 7

• Matter in this state has a definite volume, and the shape is determined by the container.
• In a liquid, the particles are attracted to one another causing them to “stick” together.
• causes liquids to have a defined volume. However, the particles are able to slowly move in random directions throughout the space they occupy.

*****Solids have a definite shape and definite volume, whereas the volume and the shape of a gas are both determined by the container.

Question 8

An ion has a 2+ charge and 18 electrons. What is the identity of the element?

Answer 8

The element is Ca.

• If an ion has a 2+ charge, then the atom lost 2 e- to form the ion.
• If the ion has 18 electrons after losing two, then it must have started with 20 electrons

Question 9

Consider the following designation for an isotope of potassium-40:

What numbers should be used for the letter “A” and the letter “Z”?

What symbol should be used for the letter “X”?

Answer 9

• Potassium-40 has a mass number of 40, which corresponds to the letter “A” and an atomic number of 19,
• which corresponds to the letter “Z.” The chemical symbol for potassium is “K”, which corresponds to the letter “X.”

A – 40

Z – 19

X – K

Question 10

Consider the following designation for an isotope of phosphorus-31:

What numbers should be used for the letter “A” and the letter “Z”?

Answer 10

• Phosphorus-31 has a mass number of 31 and an atomic number of 15.
• The mass number is always written above the atomic number and before the elemental symbol.

Question 11

Isotope

Answer 11

They are the same element with the same number of protons but a different number of neutrons, resulting in a different mass number.

Question 12

gas state defintion

Answer 12

Matter in this state has a definite volume, and the shape is determined by the container.

Question 13

how to find molecular gemotry

Answer 13

***Use the Steric Number (SN): SN = Numberofbonds + Numberoflonepairs
- Count bonds (single, double, triple) and lone pairs as separate regions of electron density.

SN = 2 → Linear → 18 0 ∘
SN = 3 → Trigonal planar → 120 ∘
SN = 4 → Tetrahedral → 109. 5
SN=5 → Trigonal bipyramidal.
SN = 6 SN=6 → Octahedral.

Question 14

Rules to Identify the Central Atom

Answer 14

1. H+ is Never the Central Atom: cause only forms one bond, so it’s always on the outside.
2. Atoms with lower electronegativity (like C) are more likely to be central because they can share their electrons more easily.
3. Oxygen, Nitrogen, or Halogens (e.g., Cl, F) Are Usually Outer Atoms:
4. If there’s one atom of a certain element (e.g., carbon in
   CH4, it’s usually the central atom.

Question 15

Single bond vs double bond

Answer 15

• A SB involves 2 e- shared between two atoms e.g H-H beacuse Each hydrogen contributes 1 electron.
• A DB involves 4 e- shared between two atoms. e.g
  C=O in carbon dioxide beacuse Carbon and oxygen each contribute 2 electrons.

Question 16

octet rule

Answer 16

-means an atom wants 8 total electrons around it
- Shared e- in bonds.
- Lone pairs (non-bonding electrons the atom “keeps” to itself).

Question 17

lone pairs using example of oxygen

Answer 17

• e- in the Outer Shell: O2 has 6 valence electrons (outer shell electrons) because it’s in Group 16 of the periodic table.
• Oxygen typically forms 2 bonds to get 8 electrons and satisfy the octet rule
• When O2 bonds with another atom, it uses some of these 6 electrons to form bonds.
• The remaining electrons that don’t form bonds stay as lone pairs.

Question 18

dipole moment

Answer 18

• an uneven distribution of electrons in the molecule.
• happens when the bonds are polar (e.g., a bond between atoms with different electronegativities).
• If the molecule’s overall geometry cancels out these polarities (symmetry), the dipole moment becomes 0.

Question 19

Electronegativity increases as you move… and examples

Answer 19

1. Across a period (left to right).
2. Up a group (bottom to top).

• Fluorine (F) is the most electronegative element.
• Oxygen ( O) , nitrogen ( N ) and chlorine ( Cl) are also highly electronegative.
• Carbon ( C ) and hydrogen ( H) have lower electronegativities.

Question 20

Pualing scale of electroneg + example of how to calc

Answer 20

Hydrogen ( H) = 2.1
Carbon ( C) = 2.5
Chlorine ( Cl) = 3.0
Oxygen ( O) = 3.5
Fluorine ( F) = 4.0 (the highest).

Subtract the smaller electronegativity value from the larger one.
For C-Cl:
Electronegativitydifference = 3.0 ( Cl ) − 2.5 ( C ) = 0.5 Electronegativitydifference=3.0(Cl)−2.5(C)=0.5 Since 0.5 > 0.4 0.5>0.4, C-Cl C-Cl is a polar bond.