Do you like chocolate chip cookies? Most of us do. Just like your chocolate chip cookie is made up of different ingredients - flour, sugar, cocoa, baking powder and chocolate chips, everything in this world is made up of different ingredients. These ingredients are called elements, and we are going to explore more about 'elements' in this lesson.
Learning Objectives
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An element is a pure substance that is made from a single type of atom and cannot be broken down into simpler chemical substances. Elements are the building blocks for all the rest of the matter in the world.
Examples of elements include iron, oxygen, hydrogen, gold, and helium.
There are 118 different elements, although only 98 of them are found naturally on Earth. All the 118 elements are represented on a standard chart of the elements called the Periodic Table of Elements. Simply put, the periodic table is a way of listing the elements. It looks like this:
Hydrogen is the most common element found in the universe. It is also the lightest element.
Helium is the second most common element in the universe but is very rare on Earth.
These gases are used in hot air balloons because they are lighter than air and can give buoyancy to balloon so that it will rise and float in the atmosphere.
Each element is represented by a one or two-letter code, where the first letter is always capitalized, and, if a second letter is present, it is written in lowercase. For example, the symbol for Hydrogen is H and the symbol for carbon is C. Some letter codes are derived from Latin terminology such as the symbol for sodium (Na) is derived from the Latin word 'natrium' which means sodium carbonate.
The chemical elements are divided into three - metals, metalloids, and non-metals.
Metals, typically found on the left side of the periodic table, are
Aluminum, iron, copper, gold, mercury, and lead are metals.
In contrast, non-metals found on the right side of the periodic table are:
Examples of elemental non-metals include carbon and oxygen.
Metalloids have some characteristics of metals and some characteristics of non-metals. The six commonly recognized metalloids are boron, silicon, germanium, arsenic, antimony, and tellurium.
The elements vary widely in abundance. In the universe as a whole, the most common element is hydrogen (about 90%), followed by helium (most of the remaining 10%). All other elements are present in relatively smaller amounts, as far as we can detect.
On the planet earth, oxygen makes up 46.1% of the mass of Earth’s crust, mostly in combination with other elements, while silicon makes up 28.5%. Hydrogen, the most abundant element in the universe, makes up only 0.14% of Earth’s crust.
The mass abundance of the nine most abundant elements in the Earth’s crust is approximately
Other elements occur at less than 0.15%
Elements found on Earth and Mars are exactly the same.
Approximately 96% of body weight consists of only four elements – oxygen, carbon, hydrogen, and nitrogen.
Calcium, phosphorus, magnesium, sodium, potassium, chlorine, and sulfur, are macronutrients or elements the body needs in a significant amount. The remaining elements are trace elements, for example, cobalt, lithium, manganese, selenium, iodine, copper, etc. These are considered to be necessary for life. Any amount of 0.01% or less is considered a trace element.
The smallest particle of an element is 'atom' and each individual atom is made up of smaller particles - electrons, protons and neutrons. The number of protons in each atom is called the atomic number. It is an important number in an element. Each element has a unique atomic number. Hydrogen is the first element and has one proton, so it has an atomic number of 1. Gold has 79 protons in each atom and has an atomic number of 79. Elements in their standard state also have the same number of electrons as protons.
If more than one type of atom is present, a substance is not an element. Compounds and alloys are not elements.
A chemical compound is a chemical substance composed of many identical molecules composed of atoms from more than one element held together by chemical bonds. For example, pure water is a chemical compound made from two elements – hydrogen and oxygen. The ratio of hydrogen to oxygen in water is always 2:1.
An alloy is a substance made by melting two or more elements together, at least one of them is metal. Examples of common alloys – Steel, a combination of iron (metal) and carbon (non-metal); bronze, a combination of copper (metal) and tin (metal); and brass a combination of copper (metal) and zinc (metal).
Similarly, a group of electrons and neutrons are not elements. A particle must contain protons to be an example of an element.
Non-elements include – water, steel, electrons and brass.
Even though elements are all made from the same type of atoms, they can still come in different forms. Depending on their temperature, they can be solid, liquid, or gas. They can also take different forms depending on how tightly the atoms are packed together. These are called allotropes. One example of this is carbon. Depending on how carbon atoms fit together, they can form diamond, coal or graphite. Sometimes, atoms of the same element have a different number of neutrons these are called isotopes. We will learn more about isotopes in a separate lesson Isotopes.
