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The structure of the atom

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Presentation on theme: "The structure of the atom"— Presentation transcript:

1 The structure of the atom
Chapter 4.3 How Atoms Differ

2 Atomic number The number of protons in an atom that identifies it as an atom of a particular element (also equals the number of electrons) Every element has a unique atomic number (unique number of protons that cannot be changed without change the identity of the element) Atomic number = number of protons = number of electrons In a neutral (no charge) atom, the number of electrons (- charge) always equals the number of protons (+ charge) The periodic table is organized left to right and top to bottom by increasing atomic number.

3 Atomic Number Problem Complete the following table:
Element Atomic Number Protons Electrons 19 35 Ne 10 K 19 19 Br 35 35 10 10

4 Mass of atoms Measured in atomic mass units (amu)
Based on carbon-12 as a standard 1 amu = 1/12 the mass of the carbon-12 atom Masses of subatomic particles: Electron = amu Proton = amu Neutron = amu

5 Mass number Mass number = number of protons + number of neutrons
How heavy the atom is Nucleus is heaviest - Contains protons and neutrons Mass number = number of protons + number of neutrons A single element can have different mass numbers if there is more than one “version” of the element – called an isotope

6 Isotopes Atoms of the same element with the same number of protons but different numbers of neutrons. The mass of isotopes increases with increasing neutrons but chemical behavior stays the same Chemical behavior is determined only by the the number of electrons that an atom has.

7 Isotope identification
Each isotope of an element is identified with the mass number Copper-63 (Cu-63): mass number = 63 (29 protons + 34 neutrons) Copper-65 (Cu-65): mass number = 65 (29 protons + 36 neutrons) Atomic Mass: the weighted average mass of all of the isotopes of a particular element This is the mass number listed on the periodic table with decimal places!!!

8 (Protons or electrons)
Isotope notation*** Isotopes are often written using a notation involving the chemical symbol, atomic number, and mass number Mass Number (Protons + Neutrons) Copper-65 63 Cu 65 Cu 29 29 Copper-63 Atomic Number (Protons or electrons)

9 Isotope problem: Determine the number of protons, electrons and neutrons for the isotopes in the table below; name each isotope and write its symbol Element Atomic Number Mass Number a. Neon 10 22 b. Calcium 20 46 c. Oxygen 8 17 d. Iron 26 57 e. Zinc 30 64 f. Mercury 80 204

10 Calculating Atomic Mass
Atomic mass: the weighted average mass of all of the isotopes of that element Mass of each isotope and isotope abundances are required to calculate this Isotope abundances Amount of element isotopes that readily exist (presented as percentages)

11 CALCULATING Atomic Mass
An element has 3 isotopes with the following mass numbers and abundances: 23A: mass 23 amu; abundance 7% 25A: mass 25 amu; abundance 76% 26A: mass 26 amu; abundance 17% (23 x 0.07)+(25 x 0.76)+(26 x 0.17) = 25.03

12 Isotope Mass (amu) Percent Abundance
Atomic Mass Problem: Calculate the atomic mass of the element X and identify the element from the periodic table knowing that it has the isotopes listed in the table below Isotope Mass (amu) Percent Abundance 54X 53.940 5.9% 56X 55.935 91.72% 57X 56.935 2.1% 58X 57.933 0.28%

13 Ion formation Ions are formed when atoms gain or lose electrons.
Positive Ion formation When an atom LOSES one or more electrons When an electron (negative charge) is lost, the ion ends up with a net positive charge (Ca – 2 e- = Ca2+) Negative Ion Formation When an atom GAINS one or more electrons When an electron (negative charge) is gained, the ion ends up with a net negative charge (O + 2 e- = O2-)

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