General Chemistry 1st Semester Review
Chapter 2 • Qualitative observation: describes matter without using numbers • Ex: • Quantitative observation: describes matter using measurements • Ex:
Classifying Matter by Composition • A substanceis matter with the same fixed composition and properties • Elements & compounds are substances • A mixtureis a combination of two or more substances in which the basic identity of each substance is not changed. • Can be separated by physical processes
Types of Mixtures • A heterogeneous mixture does not have a uniform composition and its individual substances remain distinct. • Ex:
A homogeneous mixture, or solution, always has a uniform composition and is the same throughout. • Ex: • An alloy is a solid solution that contains different metals and sometimes nonmetallic substances.
Substances: Pure Matter • There are two types of pure substances—compounds and elements.
Elements: the building blocks • An elementis the simplest form of matter • There are 117 elements – only 90 occur naturally on earth • The periodic table organizes elements and uses chemical symbols that are universally understood.
Compounds • A compoundis a chemical combination of two or more different elements joined together in a fixed proportion • Compounds have chemical formulas
Physical Properties • Physical properties are those that do not involve changes in composition. • Physical properties can be either quantitative or qualitative When salt is dropped into water, the particles in the salt crystal separate and are surrounded by water.
Physical properties are characteristics of a sample of matter that can be observed or measured without any change to its identity. • Ex:
A physical change is a change in matter that does not involve a change in the identity of the substance • Phase changes are physical changes! • Ex:
Most matter on Earth exists in one of three physical states: solid, liquid, or gas. • Changes in state are examples of physical changes because there is no change in the identity of the substance. • Some substances are volitile, or change to a gas easily at room temperature.
Chemical properties and changes • A chemical property can be observed only when there is a change in the composition of the substance • Chemical change, otherwise known as a, is the change of one or more substances into other substances.
According to the law of conservation of mass, matter is neither created nor destroyed in a chemical change
Energy & Chemical Changes • Energy, which is the capacity to do work, is either absorbed or released during a chemical change • Energy has many different forms
Exothermic vs. Endothermic • Exothermic reactions are chemical reactions that give off energy • Combustion • Endothermic reactions are chemical reactions that absorb energy • photosynthesis
Densityis the amount of matter (mass) contained in a unit of volume. • Density is a physical property
Stays the same for a given substance • Doesn’t matter how much of how little you have • Many possible units • g/m3, g/L, g/cm3, g/mL • Density formula:
Sample Problem 1 • What is the density of a substance with a mass of 24.3 g and a volume of 32.9 mL? • Answer must have correct unit
Sample Problem 2 • What is the volume of an object with a density of 125 g/mL and a mass of 281 g? • What is the mass of an object with a density of 4.36 g/mL and a volume of 500 mL?
Dalton • all elements are composed of tiny particles called atoms which CANNOT be divided into smaller parts • All atoms of the same element have identical properties. Atoms of different elements have different properties • Atoms combine in whole-number ratios to form compounds • Chemical reactions take place when atoms rearrange. Atoms of one element are NOT changed into atoms of a different element
Thomson • Discovered 1st subatomic particle! • Experiment • Discovery • Model
Rutherford • Experiment • Discovery • Model
Atomic Number & Mass Number • Atomic number = number of protons • Differences among elements result from different numbers of protons in their atoms
Mass # = Protons + Neutrons • Electrons are so small they have almost no mass • Atoms are electrically neutral • # of protons = # of electrons
Ions • Atoms with electrical charge • Cation = • Forms by: • Anion = • Forms by:
Isotopes • Atoms with the same number of protons but different number of neutrons • Oxygen – 16, Oxygen – 17, Oxygen – 18 • One isotope is more common than the others
Mass Number • Distinguishes isotopes • Protons + Neutrons = Mass Number • (Electrons have almost no mass)
Atomic Shorthand • Beryllium- - -atomic number 4 mass number 9 m# p = 4 # e = 4 # n = 5 • The atomic number is written as a subscript. • The mass number is written as a superscript. Be
P = • N = • Electron = • + ion • - ion
Atomic Mass • Different from Mass Number • Average of the masses of all the isotopes of the element • Measured in Atomic Mass Units (amu) • Proton = 1 amu • Neutron = 1 amu • Electron = 0 amu
Nitrogen has 2 naturally occurring isotopes, 147N has an abundance of 99.63%. 157N has an abundance of 0.37%. What is the atomic mass of Nitrogen?
Energy Levels • Areas of space where electrons can move • Closer to nucleus = lower energy • Further from nucleus = high energy • ELECTRONS CANNOT EXIST BETWEEN ENERGY LEVELS!!! • Numbered: level closest to nucleus = 1
S sublevel = 1 orbital • p sublevel = 3 orbitals • d sublevel = 5 orbitals • f sublevel = 7 orbitals • Each orbital can be filled: (2 e-), half filled: (1 e-), or empty: (0 e-)
Put it all together • Energy level 1 = closest to nucleus • One sublevel = s • One orbital = 1s • Energy level 2 • 2 sublevels = s and p • 4 orbitals = 2s, 2px, 2py, 2pz
Energy level 3 • Three sublevels = s, p, and d • Nine orbitals = 3s, 3px, 3py, 3pz, five 3d orbitals • Energy level 4 • Four sublevels = s, p, d, and f • 16 orbitals • Higher energy levels have all four sublevels
Sample Problems • What are the electron configurations of the following elements? • Li • O • Cl
Sample Problems • Co • Kr • Ba
Valence Electrons • Electrons in the s & p orbitals of highest energy level • Boron: 1s22s22p1 • Highest energy level • Valence electrons • Scandium: 1s22s22p63s23p64s23d1 • Highest energy level • Valence Electrons
Dot Diagrams • Valence electrons are the only ones that are involved in chemical reactions • Dot diagrams show the valence electrons
Figure out how many valence electrons element has • Write the element symbol • Add dots to top, right, bottom, and left of symbol one at a time until all valence electrons are used • Remember: each orbital can only hold 2 dots