Unit 4 Chemistry Study Guide

Early Theories of Matter

Early Theories of Matter

Who were the first people ever to propose the idea that matter was made up of particles that could not be cut up?

Leucippus and Democritus

According to Aristotle, matter was made up of...

4 elements; fire, water, earth, and air.

Alchemy

The idea where you could make gold from the 4 elements with the right proportions through experiments

Father of chemical atomic theory

John Dalton

Atoms of the same element have...

the same properties.

Atoms of the different element have...

different properties.

According to John Dalton, atoms were considered to be…

the smallest thing that existed and indestructible.

Law of Definite Proportions

A chemical compound will always contain the same elements in the same proportions by mass, no matter the size/source of the sample

Example of Law of Definite Proportions

Pure water (H2O) is always 88.8% oxygen and 11.2% hydrogen by mass, whether it is from a river or a laboratory.

Laws of Multiple Proportions

Atoms of the same element can unite in more than one ratio with another element.

Example of Laws of Multiple Proportions

H2O (water) & H2O2 (hydrogen peroxide)

Atoms (modern day)

The smallest particle of an element that still retains the properties of said element.

Was Dalton's belief that atoms were indestructible true?

No

What did J.J Thomson do?

Used a cathode ray tube to study atoms, and discovered that the charged particles were electrons.

Eugen Goldstein

Found particles flowing in the other direction, which was the first indication of positive particles, protons.

Who created the plum pudding model?

J.J. Thomson

What is the plum pudding model?

Describes the atom as a sphere of diffuse positive charge w/ negative charged electrons in it.

What did Ernest Rutherford propose?

A very small, dense, nucleus in the middle of the atom w/ electrons that surrounds the atom.

Who discovered the existence of positive charged particles, protons?

Eugen Goldstein

Who discovered the existence of electrons?

J.J. Thomson

Who discovered the nucleus?

Ernest Rutherford

Atomic Number

Atomic Number

Atomic numbers are the same as…

the number of protons

Atomic Mass

The mass of one atom of an element

Atomic Mass Unit is...

u

Fill in the blank: atoms of the same element have the same number of _____ but can have different number of ____.

Protons, neutrons

Mass number equals...

number of protons + number of neutrons

Isotopes

Isotopes

Atomic mass (Isotope)

An atomic mass of an element is the weighted average mass of the Isotope of that element

To find the atomic mass from isotopes, use the formula...

Atomic mass = (% abund) (mass) + (% abund) (mass) +...

For isotopes, what does the tiny number on the top represent and what does the tiny number on the bottom represent?

Top: Mass number

Bottom: Atomic number