Atomic Structure

Objectives

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1. Protons and neutrons exist in the nucleus, electrons exist outside the nucleus
2. Protons are positively charged, neutrons are neutral, and electrons have a negative charge
3. Relative means considered in relation or proportion to something else
4. All atomic mass is relative
5. Characterize protons, neutrons, electrons by location, relative charge, relative mass $(p=1, n=1, e= 1/2000)$

%%Atom%%- the smallest particle of an element that retains its identity in a chemical reaction

Democritus

• believed that atoms were indivisible and indestructible

John Dalton

Dalton’s Atomic Theory

• states all elements are composed of tiny indivisible particles called atoms
• atoms of the same element are identical. Atoms from one element are different from atoms from another element
• atoms of different elements can physically mix together or can chemically combine in simple whole-number ratios to form compounds
• chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one element, however, are never changed into atoms of another element as a result of a chemical reaction

%%Subatomic Particles%%- atoms can be broken down into smaller objects, which are called subatomic particles

$3 types of subatomic particles$

1. Proton
2. Neutron
3. Electron

Rutherford’s gold foil experiment

• 1911; Fired alpha particles (Helium atoms without electrons) into a sheet of gold foil
• Most of the alpha particles went straight through, some deflected at large angles
• Led to the discovery of the nucleus

https://www.youtube.com/watch?v=B-k_kMwB1zM

Atomic Mass

1. Atomic mass is based on a Carbon-12 isotope
2. $An atomic mass unit (amu) is used to describe the mass of an atom$
3. An atomic mass unit (amu) is defined as one twelfth of the mass of a carbon-12 atom

%%Neutron%%- subatomic particles with no charge that are located in the nucleus of an atom

     -==Discovered by Chadwick in 1932==

Plum Pudding Model/ Chocolate Chip Model- Thompson’s theory that subatomic particles were evenly distributed throughout the nucleus of an atom

-proven to be incorrect

%%Protons%%- positively charged subatomic particles, that are located in the nucleus of an atom

-==discovered by Goldstein in 1886==

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The atomic model

• states that the $nucleus is the central core of an atom and is composed of protons and neutrons$. The electrons are distributed around the nucleus and occupy almost all of the volume of an atom.
• improved the “chocolate chip cookie” model but was still incomplete

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