1. Elements and Atomic Structure

2. Matter Matter is defined as anything that has mass and takes up space.
Matter exists primarily in 4 states:
Solids
Liquids
Gases
Plasma
The law of conservation of matter states that matter cannot be created or destroyed, but it can change from one form to another.

3. States of Matter
Solids- arranged in a definite geometric pattern, most solids have a crystalline structure, all have a definite volume
Liquids- take the shape of their container, have a definite volume
Gases- particles are separated by large distances, do not have a definite volume or shape

4. Motion of Atoms Atoms are ALWAYS moving. So why don’t we feel them???
How do atoms move in solids, liquids and gases?
Hypothesize what causes the difference in motion between the atoms in these objects.

5. States of Matter
Plasma- a hot (greater than 5000 C), highly ionized, electrically conducting gas
Gases in a neon tube and lightening are examples of matter in the plasma state.

6. What is an element?
An element is a substance that cannot be broken down into simpler substances by chemical or physical means.
92 elements occur naturally on Earth and in the stars.

7. Compounds
Compounds are substances composed of two or more elements that are chemically combined in a fixed proportion.
BOTH compounds and elements are pure substances.
Which characteristic do they share that makes this true?

8. Mixtures
Mixtures are combinations of substances that can be physically separated.
Two classes of mixtures:
1. Homogeneous mixtures
2. Heterogeneous mixtures
What’s the difference?

9. What is an atom? An atom is an electrically neutral, spherical entity.
It is comprised of a positively charged nucleus surrounded by one or more negatively charged electrons.

10. Parts of the Atom The atom consists of 3 subatomic particles:
Proton- determines the identity of the element
Electron- determines the charge and reactivity
Neutron- affects mass only

11. Particles in an Atom Subatomic Particle Charge Mass (amu)
Location in Atom
Proton +1
Inside nucleus
Electron -1
Outside nucleus
Neutron

12. Atomic Number
The atomic number is located above the symbol of the element on the periodic table. It is represented by Z.
The number of protons in the atoms of an element is the same as its atomic number.

13. Atoms are Electrically Neutral
Since atoms are neutral in charge, the number of protons must equal the number of electrons.
Therefore, the number of electrons is determined by the atomic number also.

14. Mass Number
The mass number is located below the symbol of an element on the periodic table. It is represented as A.
Mass number =
# of protons + # of neutrons

15. Sample Problems
How many protons, electrons and neutrons are in the atoms of the following elements? Ca C Fe

16. So, where are the electrons?
The electrons reside outside of the nucleus in discrete energy levels, called shells.
The electron arrangement gives the number of electrons that can occupy each shell, or energy level.

17. Ions
When atoms gain or lose electrons, ions are formed. Electrons are lost or added to the outer energy level.
Cations are formed when atoms lose electrons. They have a net positive charge.
Anions are formed when atoms gain electrons. They have a net negative charge.

18. Example
Sodium from neutral to ion…

19. Symbolic Representations
Atomic information is often relayed in the following format:

20. Let’s Practice
Please write the atomic symbol, atomic number and mass number in atomic symbol form in your notebook for the following elements:
Silicon
Mercury
Chlorine
Lithium

21. What is an isotope?
Isotopes are atoms of the same element that have a different number of neutrons.
To distinguish between different isotopes of an element, the atomic symbol is used.

22. How do you know it’s an isotope?
The mass number indicated does NOT match the periodic table when rounded.
Example: Chlorine-37

23. Isotope Examples
State the number of protons and neutrons in the following isotopes of Neon:

24. Isotopes
It is important to remember that elements are made up of many isotopes that occur in nature.
Even though their mass numbers are different, their chemical behavior is not!!