Atomic Structure

two or more atoms; chemically bonded together

an atom is the smallest particle of an element that can take part in a chemical reaction; a molecule is a group of two or more atoms chemically bonded together

relative mass = 1; relative charge = +1

atoms contain equal numbers of protons and electrons; the positive charges from protons cancel the negative charges from electrons

electron

atoms of the same element / with the same number of protons; but with different numbers of neutrons / different mass numbers

protons = 17; neutrons = 35 − 17 = 18; electrons = 17

isotopes have the same number of electrons; chemical properties depend on the electron arrangement / number of electrons

the weighted average mass of the atoms of an element; compared to one-twelfth the mass of a carbon-12 atom

Equation used: $${A}_{r}=\frac{({\text{mass}}_{1}\times {\text{abundance}}_{1})+({\text{mass}}_{2}\times {\text{abundance}}_{2})}{100}$$ Multiply each isotope’s mass by its abundance. $$10\times 20=200$$ $$11\times 80=880$$ Sum the products and divide by 100. $${A}_{r}=\frac{200+880}{100}$$ $${A}_{r}=\frac{1080}{100}$$ $${A}_{r}=10.8$$

chlorine exists as a mixture of isotopes (³⁵Cl and ³⁷Cl) with different abundances; the Aᵣ is a weighted average of these isotopic masses, which does not have to be a whole number

Equation used: $${A}_{r}=\frac{({\text{mass}}_{1}\times {\text{abundance}}_{1})+({\text{mass}}_{2}\times {\text{abundance}}_{2})}{100}$$ Multiply each isotope’s mass by its abundance. $$63\times 69=4347$$ $$65\times 31=2015$$ Sum the products and divide by 100. $${A}_{r}=\frac{4347+2015}{100}$$ $${A}_{r}=\frac{6362}{100}$$ $${A}_{r}=63.6$$