Elements Defined by Their Numbers of Protons

An atom composed of which of these particles would have a mass of approximately 12 amu and be charge-neutral  

We have seen that atoms are composed of protons, neutrons, and electrons. However, it is the number of protons in the nucleus of an atom that identifies it as a particular element. For example, atoms with 2 protons in their nucleus are helium T FIGURE 4.8 The number of atoms, atoms with 13 protons in their nucleus are aluminum atoms, and atoms 

13 protons in its nucleus if it had a different number of protons, it would be a different element. The number of protons in the nucleus of an atom is its atomic number and is given the symbol Z. 

Most chemical symbols are based on the English name of the element. For example, the symbol for carbon is C for silicon, Si and for bromine, Br. Some elements, however, have symbols based on their Latin names. For example, the symbol for potassium is K, from the Latin kalium, and the symbol for sodium is Na, from the Latin natrium. Additional elements with symbols based on their Greek or Latin names include the following  

A The name bromine originates from the Greek word bromos, meaning stench. Bromine vapor, seen as the red-brown gas in this photograph, has a strong odor. 

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