G Chemistry

• Chemical properties describe the characteristic ability of a substance to react to form new substances, including flammability and susceptibility to corrosion
• All samples of a pure substance have the same chemical and physical properties
• Physical properties can be extensive or intensive
• Extensive properties vary with the amount of the substance and include mass, weight, and volume
• Intensive properties do not depend on the amount of the substance and include color, melting point, boiling point, electrical conductivity, and physical state at a given temperature
• Density is defined as mass per unit volume and is usually expressed in grams per cubic centimeter (g/cm^3)
• Density of a pure substance is a constant at a given temperature and pressure
• Lead has a greater density than the same volume of air
• Pure water has a density of 0.998 g/cm^3 at 25 °C
• Physical changes are changes in which no chemical bonds are broken or formed
• Physical changes involve moving molecules around, but not changing them
• Melting is an example of a physical change
• Physical changes can be reversible or irreversible
• Chemical changes occur when bonds are broken and/or formed between molecules or atoms
• Chemical changes are harder to reverse than physical changes
• Burning paper is an example of a chemical change
• Combustion of magnesium metal and rusting of iron are also chemical changes
• Energy cannot be detected directly
• Energy can only be observed through its effects on matter
• Matter is anything that has mass and takes up space
• Matter is made up of tiny units called ATOM
• Properties of matter include physical and chemical properties
• Physical properties can be measured without changing the composition of matter, such as color, texture, and odor
• Chemical properties are observed through a chemical reaction, such as radioactivity, flammability, and reactivity to acid
• Changes of matter can be physical or chemical
• Physical changes include changes of state (e.g., solidification, boiling, melting) and physical deformation (e.g., cutting of paper)
• Chemical changes involve the breaking of bonds
• Metals are good conductors, while water is a very good solvent with a specific density of 1 g/ml
• Substances can be classified based on their properties
• States of matter include solid, liquid, and gas
• Isotopes are different forms of the same element, while compounds are combinations of two or more elements
• Mixtures can be heterogeneous, homogeneous, or colloids
• Methods of separating substances include filtration, magnet, decantation, evaporation, chromatography, and distillation
• Crude oil can be separated through fractional distillation by heating and separating based on boiling temperatures
• Different properties of substances help identify their uses, such as water being a universal solvent and gold being non-reactive
• Chemical formulas include molecular formula, empirical formula, and structural formula
• Ionic compounds involve ionic bonding with a complete transfer of valence electrons between atoms (metal + non-metal)
• Covalent or molecular compounds involve covalent bonding with the sharing of electrons between atoms (non-metal + non-metal)
• An ion is an atom or group of atoms that has a net positive or negative charge
• Molecular formula - exact number of atoms