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Chemistry 2a

Atoms, Compounds and Isotopes

Electrons orbiting a central nucleus. (http://a.files.bbci.co.uk/bam/live/content/zfr2n39/small) 

Atoms comntain 3 types of particles:   PROTONS



Protons and neutrons are found in the nucleus of the atom. The electrons are arranged in shells surrounding the nucleus and different shells can hold different numbers of electrons. protons are positively charged, neutrons are neutral and electrons are negatively charged. This means that the overall charge of the nucleus in an atom is positive.

Atomic number and Mass number

The atomic number and the mass number describe an atom. You can find these numbers on the periodic table.

Chlorine 35 square from the periodic table. The mass number (35) is top-left. The atomic number (17) is bottom-left. (http://a.files.bbci.co.uk/bam/live/content/zycmsbk/small)

For example in chlorine, it's atomic number is 17 and its mass number is 35. The atomic number is equal to the number of PROTONS in the nucleus of the atom. The mass number is eqaul to the total amount of protons and neutrons. With this information you can work out the number of electrons.

35 {total number of protons and neutrons} - 17 {number of protons} =


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