2: Elements, Atoms, and the Periodic Table

1-20: 

Hydrogen, Helium, Lithium, Beryllium, Boron, Carbon, Nitrogen, Oxygen, Fluorine, Neon, Sodium, Magnesium, Aluminium, Silicon, Phosphorus, Sulphur, Chlorine, Argon, Potassium, Calcium. 

Elements that have similar chemical properties are grouped in columns called groups (or families). 

alkali metals (the first column of elements), alkaline earth metals (the second column of elements), halogens (the next-to-last column of elements), and noble gases (the last column of elements)

Each row of elements on the periodic table is called a period. 

atoms 原子

Atomic Number 原子序数

nucleus 原子核

neutrons 中子

electron 电子

proton 质子

cations阳离子 anions阴离子

isotopes 同位素

Arrangements of Electrons 

Electrons are organized according to their energies into sets called shells (labeled by the principle quantum number, n). 

Shells are further divided into subsets of electrons called subshells.