Adult woman and adult men have different percentages of water in their bodies. Men are made up of approximately 60 percent of water, while women contain about 55 percent water.

Salt has many uses. It lowers the melting point of snow or ice. It is also can remove calcium and magnesium compounds from water.

In an uncharged atom, the atomic number is also equal to the number of electrons in the atom. Neutrons have no impact on the atomic number. However, they do impact atomic mass.

Protons have 1,836 times the mass of an electron. They are found in all atomic nuclei.

In the periodic table, the number of protons and neutrons comprise the mass number. To get the number of neutrons, you subtract the number of protons from the mass number.

Deuterium is a rare from of hydrogen. It was discovered by Harold Urey in 1931. It has one proton and one neutron in its nucleus.

The word isotope comes from Greek. It is a combination of isos, which means "equal," and topos, which means "place."

Helium was first detected in the sun's corona. The element takes its name from the Greek word, "helios," which means sun.

Silver is considered a precious metal. It also has the most electrical conductivity, which makes it useful in electrical circuits.

An atom is radioactive when an unstable nucleus loses energy, resulting in the release of radiation. Elements with an atomic number 84 or higher are radioactive.

Ammonia is used as a fertilizer and in the manufacture of synthetic fabrics. It is also used as a household cleaner.

There are four basic states of matter: solid, liquid, gas and plasma. Plasma is a gas that is positively charged as opposed to a regular gas which has an equal number of protons and neutrons.

In a solid state, carbon dioxide is called dry ice. Carbon dioxide must be put under pressure at low temperatures in order to become dry ice.

There are seven noble gases. In order from top to bottom, they are helium, neon, argon, krypton, xenon, radon and oganesson.

Ions have different names depending on their charge. A positively charged ion is called a cation. A negatively charged ion is called an anion.

Electrolytes are substances that ionize in a solution. Examples of electrolytes include potassium, calcium, sodium and magnesium.

Compounds are the smallest particle of a compound that retains the chemical properties of a compound. The atoms in a molecule may be held together by covalent bonds.

Litmus tests are used to determine whether a substance is a acidic or basic. A red result means the substance is an acid. A blue result means the substance is base.

A chemical bond is the attraction between two atoms, ions or molecules. They enable the formation of chemical compounds.

"Atom" comes from the Greek word for "uncuttable." While we now know that atoms are made of protons, electrons and neutrons, a Greek named Democritus believed that atoms could not be broken up smaller. The name stuck.

The pH scale is a logarithmic scale that goes from 1 to 15. The human body is close to neutral. It has a pH of approximately 7.4.

Polar bonds are partly ionic, whereas covalent bonds have an equal sharing of electrons. Polar bonds occur between two nonmetal atoms that have different numbers of electrons.

Exothermic reactions give off energy, which causes the surrounding area to feel warmer than before. Endothermic reactions cause the surrounding area to feel cold because it has absorbed the surrounding heat.

Chemical symbols do not always match up with the current scientific name. For example, sodium has the chemical symbol Na. Sodium, which is known as natrium in Latin, is one of many elements that kept the abbreviation for its Latin name.

Mercury sulfide is a bright-red paint pigment that was used in the Paleolithic area. It is also known as cinnabar. Due to mercury sulfide's toxicity, the pigment is rarely used today.

Water holds the title "universal solvent" because it dissolves more substances than any other liquid. Water's ability to attach to both negative and positive compounds is why it is able to dissolve so many substances.

One the periodic table, alkali metals make up the first group on the far left. In order from top to bottom, the alkali metals are lithium, sodium, potassium, rubidium, cesium and francium.

Many catalysts are enzymes, which naturally occur. There are also some solid catalysts, most of which are metals. Examples of catalysts are oxides and sulfides.

Boiling points are determined using the air pressure at sea level. However, adding solutes or changing the pressure will affect the boiling point.

Potassium makes up 2.4 percent of the Earth's crust by mass, making it the seventh most abundant metal there. Each year, mines extract about 35 million tons.

Russian scientist Dmitri Mendeleev created the periodic table. He noticed a pattern in certain groups, so, in his version, he left gaps for elements that were unknown in his time.

An organic compound has carbon atoms covalent linked to other elements. However, there are some compounds that contain carbon, but are not classified as organic. Some examples are cyanides, carbonates, and carbides.

Bromine and mercury are the only elements liquid at standard temperature and pressure. Four other elements become liquid slightly above room temperature. They are cesium, Francium, Gallium and rubidium.

Masses of objects are compared to a platinum-iridium cylinder with a mass of one kilogram. The cylinder is called the International Prototype Kilogram. It is kept in Sèvres, France at the International Bureau of Weights and Measures.

Hydrogen is the lightest element. It is also highly flammable, but it needs an oxidizer and ignition source to cause a fire.