Honors Chem Quiz - Atomic Theory

Nucleus

contains a tiny fraction of the volume of an atom and contains 99.95% of its mass. Composed of protons and neutrons.

If an atom were the size of a football

the nucelus would be the size of a golfball

REAL atoms are

mostly empty space

AMU

Atomic mass unit.

1 AMU = 1.66 x 10^-24

The mass of 1 proton/ 1 neutron

1 AMU/ 1.66 x 10^-24

The number of protons

Defines the element and determines its electron configuration

proton charge

+1.6602x106-19

The number of neutrons in an atom

Equal to the mass number - the atomic number

Electron

Negatively charged particle in an atom found in the electron cloud. Determine many of the properties of matter such as reactivity.

Electron charge and mass

charge: -1.602 x 10^-19, Mass: 9.109 x 10^-31

A neutral Strontium Atom

has 38 protons and 38 electrons

An Sr2+ atom

has 36 electrons

Electron configuration

determined by the atomic number of an element.

Symbols

Proton: p+

Nuetron: N0

Electron: e-

Can two different atoms of the same element have different atomic numbers

Yes, two atoms of the same element can have different atomic numbers because they are likely different isotopes.

Isotope

Isotopes are atoms of the same element that have the same number of protons but a different number of neutrons in their nucleus, which gives them different masses.

Can two different atoms of the same element have a different number of electrons

Yes, atoms can gain or lose electrons and become ions

Ion

An atom can become an ion by gaining or losing electrons. If an atom loses electrons, it becomes a positively charged ion (cation). If an atom gains electrons, it becomes a negatively charged ion (anion).

Daltons Model

Billiards ball model - solid sphere of mass throughout

Daltons true statements

1. All matter is made of atoms

2. A chemical reaction is a rearrangement of atoms

3. Compounds are formed when atoms of different elements combine - simple whole number ratio

4.

When did Thomson publish his theory

1897-98

What instrument did Thomson use to develop his theory

Cathode ray tube

What are cathode rays

Negatively charged particles

Why do electrons move from the negative end of the tube to the positive end?

Electrons are negatively charged, they are attracted to the positive end and repelled from the negative.

Cathode Ray Tube

A glass vacuum tube in which a beam of electrons is shot. Electrons are sent from a cathode through an anode, which focuses the electrons into a thin beam. The beam has a negative charge and can be moved using a magnet.

Main conclusions of Thomsons experiment

1. Cathode rays must be negative

2. Particles that made up cathode rays are 100x smaller than a hydrogen atom

3. All different metals give of cathode rays - electrons

Thomsons model

Plum pudding model: introduced the idea of subatomic particles within the atom.

Rutherfords model

Nuclear/planetary model: electrons orbit the nucleus

Gold foil experimental set up

shooting a sheet of gold foil ( a very malleable material) with positively charged alpha particles, emitted from a source within a lead box. The foil was surrounded by a zinc screen that emmited a light whenever hit by an alpha particle

Alpha particles

a positively charged particle composed of two protons and two neutrons, which is identical to the nucleus of a helium-4 atom.

What was Rutherfords prediction

All particles would go straight through and that none would bounce back and scatter.

Rutherfords main conclusion

1. Atoms are mostly empty space

2. Positive charge is concentrated in a tiny dense nucleus

Milikans experimental set-up

An atomizer sprayed oil droplets into a chamber, where some became charged and fell between two parallel metal plates. By adjusting the voltage of the electric field to precisely balance the force of gravity. Used to find the mass and charge of an electron.

Bohr Model

An atomic model, often called the planetary model, that describes electrons orbiting a nucleus in specific, fixed circular paths called orbits or energy levels. Electrons in these orbits do not radiate energy, and can only move to a higher energy level by absorbing a specific amount of energy, or fall to a lower level by emitting that energy in the form of a photon

How did Bohr come up with his model of the atom

He built upon Rutherford's model but incorporated quantum theory, proposing electrons orbit the nucleus on a fixed path

Why is bohr's model called the planetary model

It shows electrons orbiting a central nucleus, much like planets orbit the sun.

How do electrons in the same atom differ

State of the electron: energy levels, locations, and their spin.

How many electrons can the first energy level hold

2

How many electrons can the second energy level hold

8

Mosely

Established that the elements on the periodic table should be ordered by atomic number. Based on the relationship between X-ray frequency and elements' nuclear charge.