Atoms, Elements, Compounds
Chapter 7
7.1
Structure of the Atom
Atom Structure
Smaller units
Atoms - Basic unit of matter
Retain properties
Building blocks of universe
Various kinds
Over 100 naturally occurring
Periodic table
elements
Models
Different models proposed over last 200 years
Dalton’s Model
Thomson’s Model
Rutherford’s Model
Bohr’s Model
Electron Cloud Model
Inside the Nucleus
1932, James Chadwick
Neutron
Same mass as proton
No electrical charge
Protons and neutrons
Positively charged
Strong force
Atomic Numbers and Isotopes
Atomic # = Number of protons in the nucleus of an atom
Also represents the # of electrons in the atom
Atom is neutral because + = - charges
Isotopes - atoms of the same element with different numbers of neutrons
Each element has limited # of different isotopes.
C-12 6 n, 6+, 6 e-
C-14 8 n, 6+, 6 e-
Unstable are radioactive isotopes
Mass Number and Atomic Mass
Number of neutrons affect the mass
Total # of p and n = mass number
Number written with a hyphen after the elements name
Carbon – 14, Helium – 3
Helps to distinguish isotopes
Unit used to measure mass
Atomic mass unit
amu
1/12 the mass of a carbon - 12 atom
Measurement is given as an average of the elements isotopes
Check and Explain
1. The # of p and e- of an element
2. Thomson’s – includes electrons
Rutherford’s – includes the nucleus
Bohr’s – levels of energy around nucleus
3. Both the atom’s nucleus and electron cloud contain charged particles. The atomic nucleus is positively charged; the electron cloud is negatively charged. Particles in the electron cloud move around the nucleus
4. O – 16 = 8 p, 8n, 8e-
O – 17 = 8 p, 9n, 8e-
O – 18 = 8 p, 10 n, 8 e-
7.2
ELEMENTS
Elements and Matter
One kind of atom
Can not be broken down by chemical means
Few exist pure in nature
Most combined with other elements
Eg. Na
30 play a role in everyday life
18 do not occur in nature – synthetic
Created in Lab
Properties of Elements
Luster
Texture
Color
Density
Electrical conductivity
Most solids, some liquids and gases
He, Cu, Fe, Hg, S
Chemical Symbols
Universal Shorthand
All over the world
One or two letters taken from name of element
Sometimes derived from other languages
Au - aurum, Latin for Gold
Check and Explain
An element is made up of only one kind of atom that cannot be changed.
Luster, color, density, texture, electrical conductivity
Made up of one kind of atom, equal number of protons and electrons, single atom has same properties as a large sample of that element.
7.3
Compounds
Defining Compounds
Most elements do not exist alone in nature " free "
Reactive elements
Compound – is a substance made of two or more elements chemically combined
Elements in, on, and around Earth
Living things, rocks, soil
Properties of Compounds
Different from those elements that make it up
Definite composition
Combine in specific combination
CO2, CO, NaCl, CaCO3, C3H8, SiO2
Types of Compounds
Molecular
Sharing of electrons
Most liquids and gases
CO2, NH4
Ionic
Ions
Charged particle
Combination of + and – ions
Held together by electrical charges
Most are solids
Repeating crystal structure
Usually water soluble
When melted or dissolved conducts electricity
Formulas of Compounds
Combination of symbols and numbers that represent the composition of a compound.
Subscripts – show number of each atom
More than one, written to lower right of symbol
Only one atom, no subscript is written
How do you write a formula for a compound?
Check and Explain
1.Compounds are combinations of the elements on the periodic table. There are more compounds than elements because there are many combinations of those elements.
2. Answers vary
3. Both are combinations of atoms. Ionic compounds are made up of positive and negative ions. Molecular compounds are made up of atoms that share electrons.
4. C12H22O11
7.4
Mixtures
Comparing Mixtures and Compounds
Properties of Mixtures
Types of Mixtures
Check and Explain