Chemistry Class: Matter and Periodic Table

Matter

• Pure substances contain only one type of matter; elements or compounds
• Mixtures contain multiple elements or compounds
• Compounds are two or more types of atoms bonded together
• Elements are the smallest units of matter; atoms of the same type
• Atoms in an element cannot be broken down physically or chemically

Periodic Table

• Elements arranged by increasing atomic number
• Differentiated by the number of protons in the nucleus
• Three types of elements: metals, nonmetals, and metalloids
• Metals lose valence electrons, are malleable, ductile, have luster, and conduct heat/electricity
• Nonmetals gain valence electrons, are brittle, and do not conduct heat/electricity
• Metalloids have properties of both metals and nonmetals
• Grouped by columns (groups) and rows (periods)
• Elements in the same group have the same number of valence electrons and similar properties
• Group 1 (alkali metals) have one valence electron, are highly reactive
• Group 2 (alkaline earth metals) have two valence electrons, are highly reactive
• Transition metals in the middle, multiple charges, colored ionic compounds
• Group 17 (halogens) have seven valence electrons, low melting/boiling points, not very soluble in water
• Group 18 (noble gases) have eight valence electrons, very unreactive, mostly gasses

Atomic Structure

• Protons and neutrons are in the nucleus (positively charged)
• Electrons are outside the nucleus
• Protons = atomic number
• Protons + neutrons = atomic mass
• Atomic mass - atomic number = neutrons
• Neutral atoms have equal number of protons and electrons

Atomic Structure and Location

• Atoms are mostly empty space
• Electrons are in different energy levels (further = higher energy)
• First energy level holds 2 electrons, second holds 8, third holds 18
• Energy levels contain orbitals
• Electrons absorb energy to move to a higher energy level (excited state)
• Electrons release energy (light) when returning to a lower energy level (ground state)

Calculations

• All non-zero numbers are significant

• Zeros between two non-zero numbers are significant

• Zeros at the end of a number only significant if decimal present

• Exact numbers have infinite significant figures

• Multiplication/division: answer has same number of significant figures as the least precise measurement

• Addition/subtraction: answer has the least precise place value of the measurements

• Density = mass/volume (g/mL or g/cm³)

• Percent error = |(measured-actual)/actual| x 100

• Atomic mass is average across all isotopes of an element (different versions with same number of protons but different neutrons)