Chemistry Unit 2-The Atom

Law of Conservation of Mass

mass is neither created or destroyed during chemical reactions or physical changes

Law of Definate Proportions

compound contains the same elements in exactly the same ratios by mass regardless of size

Law of Multiple Proportions

If 2 or more different compounds are composed of the same two elements, then the ratio of the masses of the 2nd element combined with a certain mass of the 1st element is always a ratio of small whole numbers

Atom

 smallest unit of an element that retains the properties of that element

Ion

atoms with uneven protons and neutrons

Nuclear Force

The attractive force that holds protons and neutrons together in the atomic nucleus.

Proton

positively charged particle found in the nucleus

Neutron

neutral charged particle in the nucleus

Electron

negatively charged particle that orbits the nucleus

Atomic Number

number of protons in an element

Isotope

atoms of the same element that have different amounts of neutrons

Mass number

total number of protons and neutrons that make up nucleus of an isotope

Nuclide

another term for nucleus

Unified Atomic Mass Unit

exactly 1/12 the mass of a carbon-12 atom

average atomic mass 

weighted average of the atomic masses of the naturally occurring isotopes of an element

Molar Mass

mass of one mole of a pure substance

What is the mass of an electron?

0.005 amu

What is the mass of a proton?

1.008 amu

What is the mass of a neutron?

1.008 amu

Who was the first person to propose the idea that matter is not divisible but made up of atomos?

Democritus

Who disagreed with Democritus because he thought that empty space could’t exist?

Aristotle

Who proposed the idea that matter is composed of atoms, are indestructible, and identical in size and chemical components?

John Dalton

What was John Dalton’s model?

“mini marble”

Who discovered the electron?

J.J. Thomson

What was Thomson’s model?

Plum pudding model

What is a cathode ray?

stream of electrons

Who discovered protons?

Ruthford and Thomson

Who did the gold-foil experiment and alpha particles?

Ruthford

Who discovered that the atom’s mass is in the nucleus?

Ruthford

Who discovered the neutron?

Chadwick

Who proposed that electrons orbit the nucleus?

Bohr

What model did Bohr create?

Solar System

Nuclide

another term for nucleus

Nucleons

all of the particles of the nucleus

Electromagnetic Force

keeps electrons near the nucleus, also the idea that opposite charges attract

Nuclear Force

keeps nucleus from breaking apart, 100x stronger than electromagnetic force

Radioactive

unstable nucleus (elements #84 and up are radioactive)

What determines if a nucleus will be radioactive?

isotopes that are located on the edge of the band of stability

What does it mean if your point is off the band of stability?

atom does not exist in nature (too unstable)

What does it mean if your point is at the edge of the band of stability?

atom is radioactive (unstable)

What does it mean if your point is on the band of stability?

atom is stable (not radioactive)

What are the 3 types of particles that unstable nucleus’ emit?

Alpha, beta, gamma

Alpha Decay

releases a helium atom with mass number of 4 and 2 protons to reduce repulsion between protons, stopped by thin barrier like paper

Beta Decay

neutron splits into an electron and a proton, electron is emitted at high speed and proton stays, new element, stopped by wood or aluminum

Gamma Decay

nucleus is at an excited state and emits a high energy photon that is a gamma particle, can penetrate through body and alter DNA

Nuclear Fission

large nucleus is split into 2 smaller nuclei, releases all 3 rays and lots of energy, used to power nuclear weapons

Nuclear Fusion 

2 small nuclei form a large, stable nucleus, little radioactive waste, takes lots of heat to get atoms to combine (how the sun makes energy and how hydrogen bombs work)

Transmutation

another term for radioactive decay into another element

What is a half-life?

time it takes for half the mass of a sample to decay (shorter half-life means more dangerous)

Diatomic

how it appears in nature