Chem Unit 2

Brownian motion

random, erratic movement of microscopic particles suspended in a fluid, caused by constant collision with surrounding molecules.

Atomistic perspective

1. matter can be divided continuously until it reaches small indestructible atoms

2. atoms differ in shape and size, moving randomly through empty space

3. atoms combine in different ways to form all matter in the universe

Anti-atomistic perspective

1. All matter was made up of 4 elements, including water, fire, air and earth.

2. matter is infinitely divisible

Who believed in atomistic perspective?

Democritus & Leucippus

Who believed the anti-atomistic perspective?

Plato & Aristotle

Law of Conservation of Mass

in a chemical reaction matter is neither created nor destroyed

• mass of reactant = mass of products

Law of Definite Proportions

A given chemical compound always contains its constituent elements in a fixed and constant ratio by mass, meaning no matter the source or how the compound was prepared, its chemical makeup remains the same.

Law of Multiple Proportions

when 2 elements form different compounds the masses of one element combining with a fixed mass of other element exist in a ratio of small whole numbers.

• explains the relationship between DIFFERENT compounds compose of the same elements

Atomic theory

1. Each element is composed of tiny, indestructible particles called atoms

2. All atoms of a given element have the same properties that distinguish them from the atoms of other elements

3. Atoms combine in simple, whole number rations to form compounds

4. Atoms of one element cannot change into atoms of another element. In a chemical reaction, atoms only change the way that they are bound together with other atoms

Plum pudding model

Thomson suggested the atom was a sphere of positive charge with negatively charged electrons embedded and uniformly distributed

Nuclear theory

1. most of an atom’s mass and positive charge is contained a smaller called a nucleus

2. Most of the volume of the atom is empty space, throughout which tiny, negatively charged electrons are dispersed

3. There are as many electrons outside the nucleus as there are protons within the nucleus so the atom is electrically neutral

Atomic number

the number is proton

Mass number

the total sum of protons and neutrons in the nucleus

Isotopes

atoms of the same element that have different neutron amounts, mass number, and physical properties

Natural abundance

the relative amounts of isotopes in a natural sample of an element

Cation

positively charged ions who have fewer electrons than protons

Anions

negatively charged ions who have more electrons than protons

Simple average

sum of all values divided by the number of values where all values are treated equally

Weighted average

sum of each value multiplied by its weight, divided by the sum of all the weights where each value has different importance

Atomic mass

the weighted average of an atom of an element, measured in atomic mass units (amu). It represents the total mass of protons, neutrons, and electrons in an atom.

Main element groups

• groups 1,2, 13-18

• properties tend to be largely predictable based on their position in the periodic table

Transition element groups

• groups 3-12

• properties tend to be less predictable based simply on their position on the periodic table

Groups

18 vertical columns, often called chemical families, containing elements with similar chemical properties.

Periods

horizontal rows on the periodic table, with 7 total periods numbered 1-7 from top to bottom.

Alkali metals

• group 1 of the periodic table excluding hydrogen

• highly reactive metals

• tend to lose 1 valence electrons

• malleable

• good conductor of heat and electricity

Alkaline earth metals

• group 2 of the periodic table

• moderately reactive metal

• tend to lose 2 valence electrons

Halogens

• group 17 on the periodic table

• highly reactive nonmetal

• poor conductors of heat & electricity

• tend to gain 1 electron

Noble gases

• group 18 on the periodic table

• colorless, odorless, tasteless, nonflammable

• nonreactive

• chemically stable

• full valence shell

Molar mass

the mass in grams of 1 mole (6.022 × 10²³ particles) of a substance, typically expressed in grams per mole (g/mol)

Mole

the SI base unit for the amount of a substance representing exactly 6.022 × 10²³ particles atoms, molecules, or ions).