Matter and the Periodic Table of Elements Study Guide
Science attempts to understand and explain our observations in nature and the universe. Chemistry, a branch of science, studies the chemical and physical properties of matter. Chemistry plays a fundamental role in understanding particular concepts of biology, physics, astronomy, geology, and other disciplines of science.Arguably, chemistry is the central science.
Matter is anything that occupies space and has mass. In other words, matter is everything in the universe. A concept map of matter is shown in Figure 1.1.
Heterogeneous mixture: A system of two or more substances (elements or compounds) that have distinct chemical and physical properties. Examples include mixtures of salt and sand, oil and water, crackerjacks, and dirt.
Homogeneous mixture (or solution): A system of two or more substances (elements or compounds) that are interspersed, such as the gases making up the air or salt dissolved in water. The individual substances have distinct chemical properties and can be separated by physical means.
Element: A substance that contains one type of atom and cannot be broken down by simple means.
Compound: A combination of two or more atoms of different elements in a precise proportion by mass. In a compound, the atoms are held together by attractive forces called chemical bonds and cannot be separated by physical means.
Molecule: A combination of two or more atoms.Molecules cannot be separated by physical means.
Atom: The basic unit of an element that retains all the element's chemical properties.An atom is composed of a nucleus (which contains one or more protons and neutrons) and one or more electrons in motion around it. Atoms are electrically neutral because they are made of an equal number of protons and electrons.
Proton: A particle that has a mass of 1 atomic mass unit (amu; 1 amu = 1.66 * 10–27 kg) and an effective positive charge of +1.
Neutron: A particle that has a mass of 1 amu with no charge.
Electron: A particle that is of negligible mass (0.000549 amu) compared to the mass of the nucleus and that has an effective negative charge of –1.
Matter can also be classified as one of four states: solid, liquid, gas, or plasma. To simplify, the discussion will be limited to solids, liquids, and gases (see Table 1.1). A solid is rigid and has a fixed volume.A liquid has a fixed volume but assumes the shape of its container. A gas has no definite shape or volume and can be compressed.
Table 1.1 States of Matter
Physical Versus Chemical Change
A physical change of a substance does not change its chemical composition. The boiling or freezing of water is an example of a physical change. It does not matter if H2O is a solid (ice), liquid, or gas (steam); it is still water. Popcorn popping is another example of a physical change. The oil heats the water in the popcorn kernel and converts the water into steam. The liquid water changing to steam causes the "explosion" and opening of the kernel, but no chemical change has occurred.
A chemical change or reaction is a process where one or more substances are converted into one or more new substances. The burning logs in a campfire are a chemical change that converts the wood (carbohydrates, etc.) into carbon dioxide, water, and other substances. The roasting of marshmallows over the campfire quickly becomes a chemical change if the marshmallows catch fire and the campfire converts its carbohydrates into carbon.