4.2 Defining the Atom • Atoms are the smallest particle of an element that retains the properties of the element. • How small are atoms? • 50 MILLION atoms in a row would take up 1cm
Structure of Atom • Atoms are made up of protons (p+), neutrons (n), and electrons (e-) • Protons = positive (+) charge • Electrons = negative (-) charge • Neutrons = neutral (no charge) • Atomic number = number of protons • Each element has ONLY ONE atomic number (# of protons)
Mass Number • Mass number = mass of the atom • Mass # = protons + neutrons Chemical Symbol Notation
Completing the Model of the Atom • Extremely dense nucleus with + protons & neutral neutrons. • Why don’t protons repel each other? • Most of the volume is empty space that electrons travel through.
4.3 How Atoms Differ • Atomic Number: number of protons (unique to each element) • For neutral atoms, #p+ = #e-
Ions are charged atoms. Lose e-’s and become positive. Gain e-’s and become negative. • F- • Ca2+
Ions & Isotopes • Ions: charged atoms (+/-) • (+) = less e- than p+ = cations • (-) = more e- than p+ = anions • Remember, you can’t change the number of p+ in an atom. You can change e- to get an ion • Isotopes: Atoms with same # of p+, but different # of neutrons • Remember, you can’t change the number of p+ in an atom. You can change n to get an isotope
How to Find Net Charge on Atom • Net charge = protons + (- # of electrons) • Ex) Carbon has a (-2) charge: 6 p+ + (-8e-) = -2 • Ex) Carbons has a (+3) charge: 6 p+ + (-3e-) = +3
Isotopes & Mass Number • Isotopes: same number protons, different number neutrons. • Ex. Potassium always has 19 p+ & 19 e- but it can have 20, 21, or 22 neutrons. • Mass Number: sum of p+ & n0.
IsotopesIn nature, most elements are found as mixtures of isotopes. Isotopes have essentially the same chemical & physical properties. Ex. Neon-22 Mass Number Atomic Number Ne 22 10
Give the # of p+, e-, and n0. SYMBOLS! • Carbon-12 • 6p+, 6e-, 6n0 • Carbon-13 • 6p+, 6e-, 7n0 • Carbon-14 • 6p+, 6e-, 8n0 12 6 13 6 14 6 C C C
Mass of Atoms • Atomic Mass Unit (amu): 1/12 the mass of a carbon-12 atom. • Protons: 1.007276 amu • Neutrons: 1.008665 amu • Electrons: 0.000549 amu • Atomic Mass: weighted average mass of the isotopes of that element. • The mass you see on the Periodic Table
Average Atomic Mass Chlorine • 76% chlorine-35 • 24% chlorine-37 • Atomic mass: 35.453 amu (mainly Cl-35) • (0.76 x 35) + (0.24 x 37) = 35.45 • Formula for finding average atomic mass: [% abundance X mass (amu)] + [% abundance X mass (amu)] = avg. mass