Ch3- Atomic Theory

4 general tenets of the atomic theory

1. All matter is composed of atoms. Atoms cannot be created or destroyed. 

2. Atoms of the same element are identical in mass and property. 

3. Atoms combine in whole-number ratios to form compounds.

4. During a chemical reaction, atoms are rearranged to form new substances. 

Dalton

credited for proposing the atomic theory, which describes the fundamental role of atoms in chemistry. 

Chemical reaction

atoms within molecules are rearranged

• Protons are positively charged subatomic particles found in the nucleus (center) of an atom. Protons weigh 1 atomic mass unit (amu). 

Neutrons are neutral (no charge) subatomic particles found in the nucleus (center) of an atom. Neutrons weigh approximately 1 atomic mass unit (amu).

Electrons are negatively charged subatomic particles found in clouds that surround an atom. The weight of an electron is negligible.

Neutrons and Protons

are used to calculate the mass of an atom

The atomic number is defined by the number of 

protons

In a neutral atom…

the number of electrons equals the number of protons

Theoretically, if a scientist could isolate 8 protons, 12 neutrons, and 5 electrons and place them on a scale, what would be the approximate total mass (in amu)

20 amu