Atoms

Atoms The smallest particle making up elements Atoms consist of three types of particles Neutrons with a neutral charge Protons with a positive charge Electrons with a negative charge Mass is measured in a.m.u. (atomic mass unit)

The positive (+) particle is called a proton + 1 a.m.u.

The neutral (no charge) particle is called a Neutron N 1 a.m.u.

The negative (–) particle is called an electron – a.m.u. 1 1840

In an atom, protons and neutrons are in the centre (nucleus) and electrons circle the nucleus in orbits or shells + N – – – – N + + + N N + + N N – Bohr Model –

Bohr model of an Atom Maximum of 2 electrons in First shell (n = 1) Maximum of 8 electrons in Second shell (n = 2) Maximum of 8 electrons in Third shell (n = 3) – – 6 P 6 N – – – –

C Periodic Table 6 number of protons and electrons Atomic number 12.011 6 Symbol Atomic Mass (average) atomic mass – atomic number = number of neutrons

Isotopes Atoms of the same element but different mass number Boron-10 (10B) has 5 p and 5 n Boron-11 (11B) has 5 p and 6 n 10B 11B

Isotopes of sodium

Isotopes and their usage Bone scans with radioactive Technetium-99 The tritium 3H content of ground water is used to discover the source of the water, for example, in municipal water or the source of the steam from a volcano.

Counting particles Protons: Atomic Number (from periodic table) Neutrons: Mass Number minus the number of protons (mass number is protons and neutrons because the mass of electrons is negligible) Electrons: If it’s an atom, the protons and electrons must be the SAME so that it is has a net charge of zero (equal numbers of + and -) If it does NOT have an equal number of electrons, it is not an atom, it is an ION.

Learning Check – Counting Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms. #p+ _______ _______ _______ #no _______ _______ _______ #e- _______ _______ _______ C 14 6 C 12 6 C 13 6 6 6 6 6 7 8 6 6 6

Learning Check – Counting An atom has 14 protons and 20 neutrons. A. Its atomic number is 1) 14 2) 16 3) 34 B. Its mass number is C. The element is 1) Si 2) Ca 3) Se D. Another isotope of this element is 1) 34X 2) 34X 3) 36X 16 14 14