Elements and Compounds Atomic Theory

1. Elements and Compounds Atomic Theory

2. Elements, Compounds, and Mixtures • Matter can be broadly classified into 3 types • Mixtures • Compounds • Elements

3. How do Different kinds of molecules differ? • Nearly all matter (molecules) we encounter in life is a mixture of substances. • Mixture = blend of 2 or more substances • Air = mixture of gases • Tap water = minerals and gases

4. What happens when a mixture is separated? • When components of mixture are separated, they are separated into pure substances. • Pure substance =constant properties and constant composition • Example: Salt water = salt + water

5. Can pure substances be divided into different categories? • Pure substances can be divided into 2 categories: compound or element

6. Elements and Compounds • Element = simplest type of matter with unique physical and chemical properties. • Element consists of only one kind of atom • Compound =type of matter composed of two or more different elements that are chemically bound together.

7. Defining the Atom • An atom is the smallest particle of an element that retains its identity in a chemical reaction.

8. Dalton’s Atomic Theory • All elements are composed of tiny particles called atoms. • Atoms of the same element are identical. 3. Atoms of different elements can physically mix in simple whole number ratios to form compounds. 4. Chemical reactions occur when atoms are separated, joined, or rearranged.

9. How do we represent atoms? • We draw circle pictures!!! • Dalton drew circle pictures to represent each kind of atom.

10. Atom & Molecule Cartoons • What’s in the box? • Individual atoms, or molecules? • Substance (pure) or mixture? • Compound, element, or both?

11. Atom & Molecule Cartoons • What’s in the box? • Individual atoms, or molecules? • Substance (pure) or mixture? • Compound, element, or both?

12. Atom & Molecule Cartoons • What’s in the box? • Individual atoms, or molecules? • Substance (pure) or mixture? • Compound, element?

13. The Nuclear Model of the Atom • Rutherford proposed: • The atom’s mass is concentrated in a tiny positive nucleus • Lightweight negative electrons circle the nucleus as planets orbit the sun • Most of the atom is empty space

14. Atomic Composition • Atoms are made up of subatomic particles:

15. Structure of Atom • Most of the volume in an atom is occupied by electrons. 2. The nucleus is the central core of an atom and it is composed of protons and neutrons.

16. Distinguishing Between Atoms • The number of protons present in an atom determines which atom you have. • Protons = atomic number. • The mass # of an atom is determined by the number of protons and neutrons. • Mass # = protons + neutrons • Neutrons = mass – protons • Not all elements are the same. • Isotopes =same element with a different # of neutrons • This is called the weighted mass average. • This system of mass based on the mass of Carbon-12.

17. mass number, A protons + neutrons  23 11 Na1+  ion charge protons – electrons atomic number, Z  protons Atomic composition • Atomic number is found on the periodic table • Mass number is NOT found on the periodic table • An atom may gain/lose electrons to form an ion • If no charge is shown, the charge is zero (a neutral atom)

18. Let’s practice

19. Isotopes • Atoms with the same number of protons but different numbers of neutrons are isotopes of the same element • 6Li and 7Li are isotopes of lithium • Both are the element lithium • 6Li has 3 protons, 3 neutrons • 7Li has 3 protons, 4 neutrons • Their chemical behaviors are identical

20. Let’s Practice • Oxygen has three naturally-occurring isotopes, with 8, 9, and 10 neutrons. Write the symbols for each of the isotopes.