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Warm-Up 9/2 • What does the atomic number of an element tell us about the element? Warm-Up 9/6 •What is the mass number of an atom equal to? Warm-up 9/7 How can you find the number of neutrons in an atom? Warm-up 9/8 • How many electrons can there be in the : • First energy level? • The second energy level? • The third energy level? The Atom • SPS1 Students will investigate our current understanding of the atom. a. Examine the structure of the atom in terms of • proton, electron, and neutron locations. • atomic mass and atomic number. • atoms with different numbers of neutrons (isotopes). • explain the relationship of the proton number to the element's identity. • SPS4 Students will investigate the arrangement of the Periodic Table. a. Determine the trends of the following: • Number of valence electrons • Types of ions formed by representative elements • Location of metals, nonmetals, and metalloids • Phases at room temperature Atom Democritus came up with the idea of an atom. (His idea wasn’t accepted much because he didn’t experiment). The word atom came from a Greek word that meant “unable to be divided”. •Atom – the smallest part of an element with all of the properties of the element Parts of the atom • Electrons: • Negative charge • Smallest particles • Located outside of atom • Protons: • Positive Charge • Located in nucleus (center) of atom Parts of the atom • Neutrons: • No charge (neutral) • Located in nucleus of atom Structure of the atom electron neutron proton Bohr’s model of the atom • He said that electrons orbited the nucleus in energy levels like planets around the sun. Modern Model of atom (wave model) • Based on probability • Says that an electron’s location can’t be determined exactly Electron Cloud Model • Another name for modern model Valence Electrons • Electrons in the outermost energy level of an atom • First level – 2 electrons • Second level – 8 electrons • Other levels can hold more electrons but are considered stable with 8 electrons Atomic Mass • The mass of an atom is measured in something called atomic mass units (amu). • The atomic mass unit is defined as 1/12th the mass of a carbon atom. Atomic Number • Atomic Number is equal to the number of protons in the nucleus of an atom. • The number of protons in an atom determines the identity of an element. Atomic Number, continued • The periodic table is arranged by increasing atomic number. • The number of protons = the number of electrons. Mass Number • Mass Number – the sum of the protons and neutrons in the nucleus of an atom Neutrons Equation: # of neutrons = mass # – atomic # Isotopes – atoms of the same element with different numbers of neutrons Isotopes More Isotopes History of the Periodic Table • Dmitri Mendeleev invented the first periodic table. He arranged it according to increasing atomic mass. • Henry Moseley arranged the modern periodic table. He arranged it according to increasing atomic number. Arrangement of Periodic Table • Groups – vertical columns, also called families – 18 groups – elements in groups have similar properties • Periods – horizontal rows, 7 periods The end.