Atom Notes


1.A physical change makes a substance look different, but is still the same substance.

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.

4.A marshmallow melting is an example of physical change. 

A marshmallow burning is an example of chemical change.


5.The ability of a substance to react chemically is called reactivity.

Reactivity refers to the chemical joining or separation of two or more substances.

7.Law of Conservation of Matter During an ordinary chemical or physical change, there is no detectable increase or decrease in the quantity of matter.


8.There are more than 116 different types of atoms - one for each element.

Differences between the atoms give the elements their different chemical properties.

The number of different combinations of atoms (making compounds) is vast. From only about 116 elements we get the millions of different materials we see around us every day.

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 (+).

A neutron is a subatomic particle with no 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.

19.Although the nucleus is very tiny, almost all of an atoms mass is in its nucleus.

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 protons than electrons, it has a positive charge.

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.

26.An atom is the smallest unit of an element that has all the properties of that element.

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.

29.In their pure form, most elements are solids at room temperature. 

A few elements, such as oxygen, nitrogen, and helium are gases.


Only mercury and bromine are liquids.

32.Two or more atoms linked together form a molecule.

About of all elements are classified as metal.

34.Some properties of a metal are: 
a) have luster (are shiny)
b) are malleable (can be hammered or rolled into sheets)
c) can conduct heat & electricity

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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