Elements And Isotopes

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Chapter 2.1, 2.2 Review Packet – Answer Key
2.1
The Nature of Matter
Lesson Summary
Atoms
The atom is the basic unit of matter, made up of three subatomic particles.
Protons have a positive charge and neutrons carry no charge. Strong forces bind protons and neutrons
together in the nucleus.
An electron is a negatively charged particle that has only about 1/1840 the mass of a proton. Electrons
constantly move around the space surrounding the atom’s nucleus.
Because an atom has the same number of protons and electrons, if it is electrically neutral.
Elements and Isotopes
A chemical element is a pure substance that consists entirely of one type of atom.
Atoms of the same element that differ in the number of neutrons are called isotopes. Isotopes are
identified by their mass number, the total number of protons and neutrons in the nucleus. Because they
have the same number of electrons in each atom, all isotopes of an element have the same chemical
properties.
Radioactive isotopes have unstable nuclei and break down at a constant
rate.
Chemical Compounds
A chemical compound is a substance formed by the chemical combination of two
or more elements in definite proportions. The physical and chemical properties of a compound are usually
very different from those of the elements from which it is formed. Scientists use formulas to show the ratio
of elements that make up a compound.
Chemical Bonds
The atoms in compounds are held together by chemical bonds. Electrons that are available
to form bonds are called valence electrons.
An ionic bond forms when one or more electrons are transferred from one atom to another, forming
ions. An atom that loses electrons becomes positively charged. An atom that gains electrons becomes
negatively charged.
A covalent bond forms when electrons are shared rather than transferred. The structure formed by
atoms joined by covalent bonds is called a molecule. The molecule is the smallest unit of most
compounds.
Atoms
THINK VISUALLY
1.
Draw the bohr model of carbon.
6p
6n
1

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