1. An atom consists of a nucleusnucleus –(of protons and neutrons) electrons in space about the nucleus.electrons in space about the nucleus. The Atom Nucleus Electron cloud

2. An atom is the smallest particle of an element that has the chemical properties of the element.An atom is the smallest particle of an element that has the chemical properties of the element. The atom is extremely small. One teaspoon of water has 3 times as many atoms as the Atlantic Ocean has teaspoons of water. The atom is extremely small. One teaspoon of water has 3 times as many atoms as the Atlantic Ocean has teaspoons of water. If a large sports stadium were an atom, a marble would represent the nucleus. If a large sports stadium were an atom, a marble would represent the nucleus.

3. ATOMIC COMPOSITION Protons (p + )Protons (p + ) –+ electrical charge –mass = 1.672623 x 10 -24 g –relative mass = 1.007 atomic mass units (amu) but we can round to 1 for mass. but we can round to 1 for mass. Electrons (e - )Electrons (e - ) – negative electrical charge – relative mass = 0.0005 amu but we can round to 0 for mass. Neutrons (n o )Neutrons (n o ) – no electrical charge –mass = 1.009 amu but we can round to 1 for mass.

4. Atomic Number, Z All atoms of the same element have the same number of protons in the nucleus, Z 13 Al 26.981 Atomic number Atom symbol AVERAGE Atomic Mass

5. Mass Number, A C-12, atom with 6 protons and 6 neutrons is the mass standardC-12, atom with 6 protons and 6 neutrons is the mass standard = 12 atomic mass units (amu)= 12 atomic mass units (amu) Mass Number (A) = # protons + # neutronsMass Number (A) = # protons + # neutrons NOT on the periodic tableNOT on the periodic table

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

7. Figure 3.10: Two isotopes of sodium.

8. Atomic Symbols Hyphen notation/mass notation - show the name of the element, a hyphen, and the mass number in sodium-23 Nuclear symbol - show the mass number and atomic number in mass number 23 Na atomic number 11

9. Isotopes? Which of the following represent isotopes of the same element? Which element? 234 X 234 X 235 X 238 X 92 93 9292

10. 1.An __ ___ is the smallest particle of an element that has the chemical properties of the element. 2. The 3 pieces of the atom are ________, _________, and _________. 3. Atoms with the same number of protons and electrons, but a different number of neutrons are called ____________. 3. Atoms with the same number of protons and electrons, but a different number of neutrons are called ____________. 4. ___________ was an English scientist who developed an atomic theory in the early 1800s.