Chemistry unit test study guide

why is chemistry a thing

H₂O(ℓ)

• way of communicating water 

• First letter (H) is always upper case 

(ℓ) 

• In liquid form 

• Not upper case 

• An “L” 

H₂O(ℓ) -> H₂O(s) 

• Physical change  

• Liquid to solid when froze 

• Substance not changed 

Physical change  

• The substance is changed to a different state 

• Substance and formula don’t change 

• Example: Au(s) -> Au(ℓ) 

• No new substance is formed 

Physical property

characteristics of a substance being measured through physical traits

Chemical change 

• Substance and formula change 

• State is changed 

• New substance is formed 

chemical property

characteristic observed through chemical reaction

Matter 

• Particles attracted to each other, creating an object 

• Occupies space and has volume 

• An atom  

• Cannot be chemically created or destroyed 

Mass and atoms 

• Cannot be chemically created or destroyed 

• Conserved in chemical change 

Solution  

• Two components  

• Solute (substance being diluted) 

• Solvent (substance that dilutes the solute) 

Symbolic  

Formulas 

Macroscopic  

• Observations 

• Visible with naked eye 

Microscopic  

• Not visible with naked eye  

• Particle theory  

Pure substance  

• Single kind of matter having predictable properties 

• Compound 

• Element  

Mixture 

• Physical combination of two or more types of substances  

• Homogenous  

• Heterogeneous  

Homogeneous  

• Cannot be physically separated

• Solution

Heterogeneous  

• Can be physically separated  

• Mechanical mixture

Mechanical mixture  

• A mixture that is visible with the naked eye 

• Example: chocolate chip cookie (dough and chocolate chips are clearly visible in the mixture), beach sand (can be separated and visible that there are multiple rocks) 

Compound  

• Can be broken down into simpler components  

• two or more types of atoms

Element  

• Cannot be broken down into other components (purest form) 

• only one type of atom

Formula of compounds 

• The element that is on the farthest left goes first (ex: HCl, hydrogen is further to the left, so it goes first) 

• A mix of two elements, element in compound  

• Covalent rule: add number before element name (ex: dichloride) 

• Ionic rule: no number before (ex: chloride) 

Bohr models 

Show the number of protons and electrons in an element 

ions

the electrical charge in an atom

Cation and anions  

• Cations are positive 

• Anions are negative  

Electrons/protons/neutrons 

• Electrons: the negative electrical charge. The atomic number  

• Protons: the positive electrical charge. The atomic number 

• Neutrons: subatomic particle that make up every atom. the mass rounded to the nearest whole number subtracted from the protons 

Isotopes  

• Atoms with the same number of protons but different number of neutrons 

• Sometimes makes mass bigger 

• Some have different physical properties 

First 18 elements 

Hydrogen, helium, lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine, neon, sodium, magnesium, aluminum, silicon, phosphorus, sodium, chlorine, argon  

Covalent  

Two atoms sharing one or more pair of electrons to hold them together 

Valence  

The outer ring, outer orbit 

Groups and periods 

• Groups are vertical

• Periods are horizontal

Ionic compounds 

• A metal and a non-metal 

• Have high melting point 

• Net charge must be 0 

• Opposite charges attract 

Molecular compounds 

• A non-metal and a non-metal 

• Both in valence shell 

• Covalent bond 

• Non-metals form molecular compounds by sharing valence shells, outer shell 

Gas test 

• If it’s oxygen, it will burn brighter 

• If it’s carbon dioxide, it will go out 

• If it’s hydrogen, it will explode