1. More on Atoms
Forces and Isotopes

2. How d0 particles in the atom stay together?
The four forces in an atom
How d0 particles in the atom stay together?
Four Forces

3. Remember—Atoms of different Elements are different structurally
Atom’s are identified by their Atomic Number If you know the number of protons(atomic number), then you can identify the atom on the periodic table.

4. Why are all Atoms are Electrically Neutral?
If an atom gains or loses electrons the atom is no longer neutral .
Normally in an atom the number of electrons within the electron cloud is equal to the number of protons in the nucleus. The positive and negative charges cancel each other out. Therefore, the atom is said to be electrically neutral.

5. Valence Electrons can move on or off atoms.
Electrons in the outer shells can move. All electrons in the outer shell are called VALENCE Electrons.
Valence Electrons can move on or off atoms.
Atoms can gain or lose electrons in the outer shell. Then they have a charge and are no longer neutral—the atom is now an ion.
This gaining or losing of electrons happens when atoms form molecules.

6. Atoms can also be changed by
Changing its mass

7. How do we change the mass of an atom?
The mass of an atom is measured by the mass of the protons and neutrons. Protons and Neutrons have about the same mass each =1amu

8. Changing an Atom’s mass doesn’t change its identity.
All atoms of an element have the same number of protons but the number of neutrons can vary. This change in neutron number forms an isotope.

9. Atomic Mass and Mass Number
Decimal No Decimals

10. Atoms with the same number of protons and differing numbers of neutrons are called ISOTOPES.
12 P and 12N =
12 P and 13N
with

11. Hydrogen and Hydrogen--1

12. Isotopes X Neon - 20 Magnesium - 22 Neon - 22
4.3 Q
- atoms of the same element with different # of n0 !!!
Three isotopes of Carbon:
Carbon - 12
(6p+, 6n0)
element of life
extremely rare
radioactive…carbon dating
Carbon - 13
(6p+, 7n0)
Carbon - 14
(6p+, 8n0)
-Compare to Atomic Mass Number:
Which of the following are isotopes of the same element?
Neon - 20
Neon - 22
Magnesium - 22 22 X 12 10 25
Same # of protons/atomic number

13. So Changing the number of Neutrons:
Changes the mass of the atom, but doesn’t change the atom’s properties.
Some Isotopes are unstable. The nucleus of unstable atoms do not hold together well.
Radioactive decay is the process whereby the nucleus of unstable isotopes release fast moving particles and energy. EX. Carbon dating

14. Atoms of the same element can be different from each other.
2. Creating Isotopes by changing the mass of the atom by altering the number of neutrons. Proton number does not change!!!!!!!!!