Study Guide for Elements, Compounds, and Chemical Bonding
An Element is a pure substance that can not be separated into simpler substances by physical or chemical means.
A pure substance is a substance in which there is only one type of particle. So, each element contains only one type of particle. These particles, called atoms are much too small for us to see. For example, every atom in a 5 g nugget of the element gold is like every other atom of gold. The particles of a pure substance are alike no matter where they are found.
Properties of Elements
- Each element can be identified by its unique set of properties. For example, each element has it's own characteristic properties.
- These properties do not depend on the amount of the element present.
- Characteristic properties include some physical properties, such as boiling point, melting point, and density.
- Chemical properties, such as reactivity with acid, are also characteristic properties.
Classifying elements by their properties
- Elements are grouped into categories based on the properties that they
share.
- There are three major categories of elements. They are
Metals- which are shiny, malleable, ductile, conduct heat and electric current.
Nonmetals- which are dull and cannot conduct heat or electric current.
Metalloids- which have properties of both metals and nonmetals; some are
semi-conductors, some are shiny, some are dull, some are somewhat malleable
and ductile. Some conduct heat and electric current.
Arranging the Elements
- Dmitri Mendeleev developed the first periodic table of the elements by listing them in order according to their atomic mass. He used his table to predict that elements with certain properties would be discovered later.
- The properties of elements repeat in a regular, or periodic pattern.
- The periodic law states that the repeating chemical and physical properties of elements relate to and depend on elements' atomic numbers
- Moseley rearranged the elements in order of increasing atomic number. This is the arrangement of the present periodic table that we now use.
- Elements in the periodic table are classified as metals, nonmetals, and metalloids.
- Each element has a chemical symbol.
- A horizontal row of elements is called a period.
- Physical and chemical properties of elements change across each period.
- A vertical column of elements is called a group or family. Elements in a group usually have similar properties.
Compounds
- A compound is a pure substance composed of two or more elements.
- Compounds have chemical formulas.
- The elements that make up a compound always combine in a specific ratio according to their masses.
- Each compound has a unique set of physical and chemical properties.
- Water is a compound with unique properties. All living things rely on water for life.
- Compounds can be broken down into simpler substances only by chemical changes.
- A molecule is the smallest unit of a compound that has all the properties of the compound.
- The make-up of a molecule is shown in a chemical formula.
- A chemical formula uses chemical symbols and subscripts to identify the number of atoms of each element in a molecule of a compound.
- Compounds make up the food you eat, the school supplies you use and
even the clothes you wear.
- Proteins are compounds found in all living things. The element nitrogen is
one of the elements needed to make proteins.
- Plants use nitrogen compounds that are in the soil. Animals get the
nitrogen they need by eating plants or animals that have eaten plants. The
proteins in the food are broken down as an animal digests the food. The
simpler compounds that form are used by the animal's cells to make new
proteins
Atoms: The Building Blocks of Compounds
An atom is the smallest unit of an element that has all of the properties of the element. Atoms are the building blocks of matter. To understand how elements join together as compounds, you must understand the structure of an atom.
• Everything is made up of matter
• An element is matter that is made up of only one kind of atom.
• An atom is the smallest particle of an element.
• Atoms give an element its chemical and physical properties.
• The size of an atom varies with the element.
• John Dalton, an English scientist, proposed that atoms were solid spheres.
• However it is now known that most of an atom is empty space.
• An atom is made up of 3 types of particles; called subatomic particles.
The subatomic particles are Protons, Neutrons, Electrons
• The Nucleus of the atom contains the protons and the neutrons
• The Protons have a positive charge, the neutrons have no charge; they
are neutral
• Electrons are found in the energy levels surrounding the nucleus, electrons are negative.
• Maximum Number of Electrons in Each Energy Level
First energy level can hold up to 2 electrons.
Second energy level can hold up to 8 electrons.
Third energy level can hold up to 8 electrons.
Each energy level after has a maximum number of electrons.
• How do we diagram the atoms of an element?
The Atomic number tells us the number of protons in a nucleus of an atom, in
neutral atoms the atomic # also tells us the number of electrons.
The Atomic Mass tells us the total number of protons and neutrons in a
nucleus of an atom.
