Download Elements Elements (cont.) Elements (cont.) Dalton`s Atomic Theory

Elements
• Over 112 known: 88 found in nature, others
are man made.
Chapter 4
Chemical Foundations:
Elements, Atoms,
and Ions
• Each element has a unique one- or
two-letter symbol
Copyright © Houghton Mifflin Company. All rights reserved.
Elements (cont.)
Copyright © Houghton Mifflin Company. All rights reserved.
4|3
Elements (cont.)
4|4
Dalton’s Atomic Theory
Copyright © Houghton Mifflin Company. All rights reserved.
4|5
Dalton’s Atomic Theory
• Elements are composed of tiny particles called atoms.
• All atoms of a given element are identical.
• Atoms of different elements combine to form
compounds.
– All carbon atoms have the same chemical and physical
properties.
• Atoms of a given element are different from those
of any other element.
– Carbon atoms have different chemical and physical
properties than sulfur atoms.
Copyright © Houghton Mifflin Company. All rights reserved.
4|6
Copyright © Houghton Mifflin Company. All rights reserved.
4|7
1
Dalton’s Atomic Theory
Formulas Describe Compounds
• Law of Constant Composition: all samples of a
compound contain the same proportions (by mass) of
the elements that form the compound.
• Atoms are indivisible by chemical processes.
– All atoms present at beginning are present at the end.
– Atoms are not created or destroyed, just rearranged in
chemical reactions.
– Atoms of one element cannot change into atoms of
another element.
• A compound is a distinct substance that is
composed of atoms of two or more elements.
• Compounds are identified by the number and type
of each atom in the simplest unit of the compound.
– Molecules or ions
• Cannot turn lead into gold by a chemical reaction
Copyright © Houghton Mifflin Company. All rights reserved.
4|8
Molecular and Ionic Compounds
Copyright © Houghton Mifflin Company. All rights reserved.
4|9
Writing Formulas of Compounds
• Each element is represented by its symbol.
• The number of each type of atom is indicated by a
subscript written to the right of the element
symbol.
• If only one atom is present, do not include a
subscript.
• If polyatomic groups are present in the molecule,
they are written inside parentheses if more than
one group is present.
• Examples: H2O, NaCl, KNO3, Mg(NO3)2
Copyright © Houghton Mifflin Company. All rights reserved.
4 | 10
What Are Atoms Made Of?
4 | 11
The Electron
• J.J. Thomson investigated a beam called a
cathode ray.
• Tiny, negatively charged particle
• Very light compared to mass of atom
– 1/1836th the mass of a H atom
• He determined that the ray was made of tiny
negatively charged particles we now call
electrons.
Copyright © Houghton Mifflin Company. All rights reserved.
Copyright © Houghton Mifflin Company. All rights reserved.
• Move very rapidly within the atom
• Atoms of different elements all contain
electrons
• Discovered by J.J. Thomson
4 | 12
Copyright © Houghton Mifflin Company. All rights reserved.
4 | 13
2
The Proton
Rutherford’s Gold Foil Expt
• If negative electrons exist, must also
have positive particles to balance the
charge and make the atom electrically
neutral
• Assume “Plum Pudding Model” electrons suspended in a positively
charged electric field
Copyright © Houghton Mifflin Company. All rights reserved.
4 | 14
Rutherford’s Nuclear Model
Copyright © Houghton Mifflin Company. All rights reserved.
4 | 15
Components of an Atom
• The atom contains a tiny dense center called
the nucleus.
– The volume is about 1/10 trillionth the volume
of the atom.
• The nucleus is essentially the entire mass
of the atom.
• The nucleus is positively charged.
– The amount of positive charge of the nucleus
balances the negative charge of the electrons.
• The electrons move around in the empty space
of the atom surrounding the nucleus.
Copyright © Houghton Mifflin Company. All rights reserved.
4 | 16
The Modern Atom
Copyright © Houghton Mifflin Company. All rights reserved.
4 | 17
The Modern Atom (cont.)
• Atoms are composed of three main pieces:
protons, neutrons, and electrons.
• The nucleus consists of protons and neutrons.
Copyright © Houghton Mifflin Company. All rights reserved.
4 | 18
Copyright © Houghton Mifflin Company. All rights reserved.
4 | 19
3