Understanding Matter: Properties, Changes, and Reactions

Posted on Feb 17, 2025 in Chemistry

Chemistry Basics

► Chemistry: The study of the properties and transformations of matter. ► Matter: Anything that has mass and occupies space – things you can see, touch, taste, or smell. ► Property: A characteristic that can be used to describe a substance. Substances have both physical and chemical properties. ► Transformations: A change in the properties of matter with time. There are physical changes and chemical changes.

Properties of Matter

Matter has both physical and chemical properties.

Physical Properties

Density, color, and melting point are physical properties of matter. Observing a physical property can be done without altering the makeup of a substance.

Chemical Properties

Chemical composition (what matter is made of), chemical reactivity and how matter behaves are chemical properties. Observing a chemical property alters the substance.

Changes in Matter

Physical Change

Does not alter the chemical makeup of a substance. ►Chemical reactivity is unchanged. ►Changes in state, changes in particle size, and the formation / separation of mixtures are all examples of physical change. ►Melting of ice to form liquid water is a physical change. In this case only a change in form takes place. The chemical makeup of the substance remains H2O.

Chemical Change

Alters the makeup of a substance. ►Reactivity changes with the formation of new substances. ►Heat, light, or electrical energy is often emitted or absorbed. ►Potassium reacting with water is an example of a chemical change.

States of Matter

  • ►Solid: A substance that has a definite shape and volume. Solids are rigid and dense.
  • ►Liquid: A substance that has a definite volume but that changes shape to fill the container. Liquids are dense and fluid.
  • ►Gas: A substance that has neither a definite volume nor a definite shape. Gases are low density fluids.

Substances can exist in each of these three states depending on the pressure and the temperature. ►The conversion of a substance from one state into another is known as change of state.

Classification of Matter

Matter is classified as either pure substances or mixtures.

Pure Substance

Matter that is uniform in its chemical composition and properties.

  • • Element: Pure substance that can not be broken down chemically into simpler substances.
  • • Chemical Compounds: Two or more elements combined chemically in specific ratios to form a pure substance.

Mixture

A blend of two or more pure substances in any ratio each retaining their identity.

  • • Homogeneous mixture – A uniform mixture that has the same composition throughout.
  • • Heterogeneous mixture – A non-uniform mixture that has regions of different composition.

Chemical Elements and Symbols

118 elements have been discovered. ►91 occur naturally, 27 are produced artificially ►A one- or two-letter shorthand is used for each element.

  • • The first letter is always capitalized.
  • • The second letter, if any, is always lowercase.

►Most of the symbols are based on the elements commonly used names. ►A few symbols are based on Latin names for the elements ►Each element has its own unique symbol. One or two letter symbols are used to represent elements. The first letter is always capitalized and the second letter is always a lower case. Examples: C, Cr, P, Pb ► Most symbols are derived from modern names and are easy to remember. Examples: H‘ for hydrogen, O for oxygen, N for nitrogen, etc. Not all elements occur with equal abundance.

Chemical Formula

A notation for a chemical compound using symbols and subscripts to show how many atoms of each element are present. When no subscript is given for an element a subscript of ‘1’ is understood.

Periodic Table

Large amounts of information regarding the properties of elements are embedded in the periodic table. Elements are roughly divided into 3 groups:

  • ► Metals: Found on the left side of the table.
  • ► Nonmetals: Found on the right side of the table.
  • ► Metalloids: Found along a diagonal line between metals and nonmetals.

Metals

  • ►They 94 of the known elements
  • ►Occur on the left side of the periodic table
  • ►Solid at room temperature (except mercury)
  • ►Usually lustrous when freshly cut
  • ►Good conductors of heat and electricity
  • ►Malleable rather than brittle

Nonmetals

  • ►18 of the known elements
  • ►Occur on the right side of the periodic table
  • ►11 are gases, 6 are solids,1 (bromine) is a liquid.
  • ►Poor conductors of heat and electricity
  • ►Brittle when solid

Metalloids

  • ►6 of the known elements
  • ►Properties are intermediate between metals and nonmetals.
  • ►Occur in a zigzag band between metals on the left and nonmetals on the right side of the periodic table

Chemical Reactions

An Example of Chemical Change — ►Nickel is a hard, shiny metal. ►Hydrogen chloride is a colorless gas that dissolves in water to form hydrochloric acid. ►When nickel is added to hydrochloric acid; the nickel is eaten away; the solution turns green; and a gas bubbles out. ►When nickel is added to hydrochloric acid; the nickel is eaten away; the solution turns green; and a gas bubbles out. ►A chemical reaction is taking place. This is indicated by: •Change in color •Dissolving of nickel •Appearance of bubbles

  • Reactants: One or more starting materials. Between reactants, the “+” can be read as ‘reacts with’.
  • ►Between products and reactants, the ->‖ can be read as “to form”.
  • Products: One or more substances formed as a result of a chemical reaction. Between products, the “+” can be read as “and”.

Physical Quantities

►Mass, volume, temperature, density, and other physical properties are called physical quantities and are described by both a number and a unit: ►Physical quantity—A physical property that can be measured. ►Unit—A defined quantity used as a standard of measurement. ►Numbers without units are meaningless in the sciences

►Units of measure that combine one or more other measurements are called derived units. • Speed: meters per second (m/s) • Density: grams per cubic centimeter (g/cm3 ) • Area: square meters (m2 ) ► Unit sizes are often inconveniently large or small, so they can be modified using prefixes to refer to smaller or larger quantities.

Measuring Mass, Lengths, and Volume

  • ►Mass—A measure of the amount of matter in an object.
  • ►Weight—A measure of the gravitational force that the earth or other large body exerts on an object.
  • ►The meter is the standard measure of length, or distance, in the SI and metric systems.
  • ►Volume is the amount of space occupied by an object. The SI unit for volume—the cubic meter, m3—is so large that the liter (1 L = 0.001 m3 ) is much more commonly used.

Rules for Significant Figures

  • ►Rule 1: Zeros in the middle of a number are like any other digit; they are always significant.
  • ►Rule 2: Zeros at the beginning of a number are not significant; they act only to locate the decimal point.
  • ►Rule 3: Zeros at the end of a number and after the decimal point are significant. It is assumed that these zeros would not be shown unless they were significant.
  • ►Rule 4: Zeros at the end of a number and before an implied decimal point may or may not be significant.

RULE 1: In carrying out a multiplication or division, the answer cannot have more significant figures than either of the original numbers. Rule 2: In carrying out an addition or subtraction, the answer cannot have more digits after the decimal point than either of the original numbers.

Conversion Factors

How many feet are in 1.23 miles? There are 5280 feet in one mile. 1. Begin by writing a question mark and then the UNIT you are looking for followed by an equal sign. 2. After the equal sign, write the number and unit you are GIVEN in the problem and put that over 1. 3. Write down the relationship(s) between the two units in a separate area of the page. 4. Write the times sign and then a line. 5. Write the UNIT of the GIVEN quantity below the line you just drew. Leave room to write a number in front of this unit 6. Write the UNIT that you are looking for on top of the line. Leave room to write a number in front of this unit. 7. Add numbers in front of the units that state the relationship for the units. 8. Cross out the units that appear on the top and bottom of the equation. 9. Perform the necessary calculations and express your answer with the correct number of significant figures and units.

Temperature

Temperature is commonly reported either in degrees Fahrenheit (oF) or degrees Celsius (oC). ► The SI unit of temperature is the Kelvin (K). ► 1 Kelvin, no degree, is the same size as 1 oC. ► 0 K is the lowest possible temperature, 0 oC = 273.15 K is the normal freezing point of water. To convert, adjust for the zero offset. ► Temperature in K = temperature in oC + 273.15 ► Temperature in oC = temperature in K – 273.15

► 212 oF – 32 oF = 180 oF covers the same range of temperature as 100 oC – 0 oC=100 oC covers. ► Therefore, a Celsius degree is exactly 180/100 = 1.8 times as large as Fahrenheit degree. ► Using the freezing point of water as a reference, the scales are offset by 32 degrees.

Energy

The capacity to do work or supply heat. ► Energy is measured in SI units by the Joule (J), the calorie is another unit often used to measure energy. ► One calorie (cal) is the amount of heat necessary to raise the temperature of 1 g of water by 1°C. ► A kilocalorie (kcal)= 1000 cal. A Calorie, with a capital C, used by nutritionists equals 1000 cal.