A chemical change changes the substance into something else.
A change in color or the production of light, heat, or gas may indicate that a chemical change has occurred.
A marshmallow burning is an example of chemical change.
Reactivity refers to the chemical joining or separation of two or more substances.
Differences between the atoms give the elements their different chemical properties.
About 5,000,000 atoms could be lined up across the period at the end of a sentence.
The nucleus is the very tiny center of an atom.
The nucleus is made up of protons and neutrons.
A proton is a subatomic partial with a positive charge (+).
The rest of the atom is made up of electrons, which surround the nucleus.
An electron is a subatomic particle with a negative charge (-).
The paths in which the electrons move are called orbits.
They are also referred to as energy levels.
The mass of a proton is nearly 2000 times the mass of an electron.
Protons and neutrons have about the same mass.
Electrons and protons have charges that are equally strong.
If an atom has more electrons than protons, it has a negative charge.
An atom with the same number of protons and electrons is called a neutral atom.
Each element has an atomic number, which is the number of protons in its nucleus.
The number of protons in a hydrogen atom for example is one. So, the atomic number for hydrogen is 1.
A few elements, such as oxygen, nitrogen, and helium are gases.
Only mercury and bromine are liquids.
About ¼ of all elements are classified as metal.
In the modern periodic table, elements are arranged in order of atomic number.
They are also arranged so that elements with similar properties are in the same column.
Elements in the same group often have the same number of electrons in the outer energy levels.
The arrangement of electrons gives elements their chemical properties.
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