What makes up 99 of the mass of an atom

Its atomic mass is Improve this page Learn More. Skip to main content. Module 2: Chemistry of Life. Search for:. Atoms Learning Outcomes Draw a diagram of an atom, according to current scientific understanding.

Practice Question Carbon has an atomic number of six, and two stable isotopes with mass numbers of twelve and thirteen, respectively. Figure 2. Carbon and carbon Show Answer Carbon has six neutrons.

Carbon has seven neutrons. Try It. Did you have an idea for improving this content? Licenses and Attributions. Thus, since the atomic mass of iron is The same concept can be extended to ionic compounds and molecules. One formula unit of sodium chloride NaCl would weigh One molecule of water H 2 O would weigh The Nuclear Force. Inside the nucleus all the electric forces are repulsive because the protons repel each other, and the neutrons don't feel any electric force.

How then is the nucleus held together? There is another force, called the nuclear force , that is mostly attractive and acts between two protons, between two neutrons, and between a neutron and proton. In nuclei this force is stronger than the repulsive electric force and so nuclei are held together. Atoms, Molecules, and Matter in Bulk. It is possible to have a system with N e not equal to N p , but then it is not called an atom; it is called an ion.

On earth most of the matter we come in contact with is made of atoms. However, in the sun and the stars most of the matter is in the form of ions. It is probable that most of the matter in the universe is in the form of ions. The number of neutrons in the nucleus is in many cases approximately equal to the number of protons. A small number of atoms may combine to form a molecule such as water H 2 O or carbon dioxide CO 2.

The arrangements and rearrangements of atoms in molecules form the domain of chemistry. A solid consists of a regular array or lattice containing a very large number molecules or atoms. A typical number of atoms in a piece of matter on a human scale is 10 Physical properties of matter include hardness, malleability, color, and melting point.