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Important Vocabulary
atom: a small particle that is the building block of matter.
element: a substance that consists of only one type of atom.
compound: a substance containing atoms of two or more different elements connected together.
molecule: two or more atoms that are held together and that act as a unit.
periodic table: a chart of the elements arranged into rows and columns according to their physical and chemical properties.
chemical symbol: one or two letters that represent an element.
chemical formula: a group of chemical symbols and numbers that represent the elements and the number of atoms of each element that make up a compound or a molecule.
Lesson 1.1 Elements and Compounds
Lesson 1.1 Elements and Compounds
Elements and Compounds
You might recall that states of matter are made of particles called atoms. An atom is a small particle that is the building block of matter. An atom is almost too small to imagine. Think about how thin a human hair is. The diameter of a human hair is about a million times greater than the diameter of an atom. Even though atoms are so tiny, they determine the properties of the matter they compose.
Elements
Some substances, such as gold, are made of only one kind of atom. Others, such as sodium chloride, are made of more than one kind of atom. An element is a substance that consists of only one type of atom. All atoms of an element are alike, but atoms of one element are different from atoms of other elements. For example, the element gold is made of only gold atoms, and all gold atoms are alike. But gold atoms are different from silver atoms, oxygen atoms, and atoms of every other element. Because there are 118 known elements, there are 118 different types of atoms. Each element has many properties. No two elements have all of the same
Diatomic Elements
The atoms of most elements exist as individual atoms. For example, a roll of purealuminum foil consists of trillions of individual aluminum atoms. However, the atoms of some elements usually exist in groups. For example, the oxygen atoms in air exist in pairs. Elements that are traditionally found in pairs are called diatomic elements.Diatomic elements are more stable in pairs than as single atoms. Hydrogen, nitrogen,
oxygen, fluorine, chlorine, bromine, and iodine are the seven diatomic elements. Whether the atoms of an element exist individually, in pairs, or in groups, each element contains only one type of atom. Therefore, its composition is always the same.
Compounds
Does it surprise you to learn that there are only 118 different elements? After all, if you think about all the different things you observe each day, you could probably name many more things than that. Why are there so many different things when there are only 118 elements? Most matter is made of atoms of different types of elements connected together. A compound is a substance containing atoms of two or more different
elements connected together. Pure water (H2O) is a compound because every sample of pure water contains atoms of hydrogen and oxygen in the same combination—two hydrogen atoms to one oxygen atom. There are many different things because elements can join together to form compounds.
Properties of Compounds
How would you describe sodium chloride, or table salt? The properties of a compound, such as table salt, are usually different from the properties of the elements from which it is made. Table
salt, for example, is made of the elements sodium and chlorine. Sodium is a soft metal, and chlorine is a poisonous, green gas. These properties are very different from the table salt you sprinkle on food! A compound often has different properties from the individual elements that compose it
Molecules
You might recall that a molecule is two or more atoms that are held together and that act as a unit. Is a molecule the smallest part of a compound? For many compounds, this is true. Many compounds exist as molecules. An example is water. In water, two hydrogen atoms and one oxygen atom always exist together and act as a unit. Carbon dioxide (CO2) and table sugar (C12H22 O11) are also examples of compounds that are made of molecules. However, some compounds are not made of molecules. In some compounds, such as table salt, or sodium chloride, no specific atoms travel together as a unit. Table salt (NaCl) is still a substance because it always contains only sodium (Na) and chlorine (CI) atoms.
One grain of table sugar is made up of trillions of sugar molecules. Imagine breaking a grain of sugar into the tiniest microscopic particle possible. You would have a molecule of sugar. Each sugar molecule is composed of 12 carbon atoms, 22 hydrogen atoms, and 11 oxygen atoms all connected together. The only way to further break down the molecule would be to chemically separate the carbon, hydrogen, and oxygen atoms. These individual atoms have very different properties from the compound sugar.
Chemical Symbols
Recall that symbols of elements are shown in the periodic table. For example, the symbol for carbon is C. The symbol for copper is Cu. Each element can exist as just one atom or, in the case of the diatomic elements, two atoms of the same element. A chemical symbol is one or two letters that represent an element.
These letters do not always match the element name on the periodic table because the symbols are often an abbreviation of the element's name in a different language, traditionally Latin. For example, sodium’s chemical symbol is Na, because the symbol came from the Latin word natrium. When writing an element's chemical symbol, the first letter is always capitalized, and the second letter, if present, is always lowercase. While element names can be different in each language, chemical symbols are universally understood.
Chemical Formulas
Just as elements have chemical symbols, compounds and molecules have chemical formulas. A chemical formula is a group of chemical symbols and numbers that represent the elements and the number of atoms of each element that make up a compound or a molecule. These numbers are called subscripts. Subscripts can be found to the right of the chemical symbol and are smaller in size. A subscript, or small number after a chemical symbol, shows the number of atoms of each element in the compound. If no subscript is written after a symbol, only one atom of that element is present in the chemical formula. For example, carbon dioxide (CO2) is made up of one carbon atom and two oxygen atoms.
Mini Lesson
Atoms for kids is an introduction video that helps students learn all about atoms. We answer questions like "What is an Atom?", "What is an Atom made of?", and "What do Atoms do?". We explore protons, electrons and neutrons and give a brief overview of the periodic table of elements.
What you will learn in Periodic Table of Elements for Kids:
0:00 Introduction to the Periodic Table of Elements 0:25 What is an element?
1:28 Atomic number = number of protons
2:18 How Dmitri Mendeleev organized the elements
3:19 Chemical elements arranged into periods and groups
4:08 What you can learn from Periodic Table of Elements
5:02 Where elements get their chemical symbols
6:03 Specific information you can find for each element on the table
6:54 Review of the facts
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