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Atomic Structure Part 2 History of the Atom Democritus (Greek 460-370 BC) • 1st to use the word atom • Believed that atoms were indivisible & indestructible • No scientific support Aristotle (Greek 384-322 BC) • Rejected the theory of atoms • Believed in 4 core elements fire, air, water, earth Subatomic Particles 3 types of subatomic particles • Protons: Positively charged particle (+) found in the nucleus. • Neutrons: Uncharged particle also found in the nucleus. • Electrons: Negatively charged particle (-) that moves around the outside of the nucleus in the electron cloud. What makes atoms different from one another? # of protons Atomic number = # of protons in the atoms nucleus. The atomic number determines the identity (what is it) of the atom. How do you determine the # of neutrons? Atomic mass = total number of # protons and # neutrons in an atom’s nucleus. Not all atoms of an element have the same atomic mass number. # of neutrons = atomic mass – atomic number What is the atomic mass of helium? 4.0026… round to 4 What element has an atomic mass of 27? Aluminum How many protons does this element contain? 13 How many neutrons does this element contain? 27 – 13 = 14 Isotopes Atoms of the same element that have different numbers of neutrons in the nucleus. The number of protons and electrons are the same. Symbols: 23 or Na 11 24 Na 11 12 or C13 or C 6 6 14 C 6 Ions Formed when an atom gains or loses one or more electrons. Occurs 2 ways: • Positive Ion (+) • Atom loses one or more electrons • More protons than electrons, results in a (+) charge • Negative Ion (-) • Atom gains one or more electron • More electrons than protons, results in a (-) charge Examples of Ions H+ ClAs3Mg2+ Lost 1eGained 1eGained 3eLost 2e-