Chapter 2
Atoms and the Periodic Table / Elements and the Periodic Table * An element is a pure substance that cannot be broken down into simpler substances by a chemical reaction.
* Each element is identified by a one- or two-letter symbol.
* Elements are arranged in the periodic table.
* The position of an element in the periodic table tells us much about its chemical properties.
Atoms and the Periodic Table / Elements and the Periodic Table
Atoms and the Periodic Table
Atoms and the Periodic Table / Metals, Nonmetals, and Metalloids * The elements in the periodic table are divided into three groups—metals, nonmetals, and metalloids.
Metals:
* are located on the left side of the periodic table
* usually exist as shiny solids * are good conductors of heat and electricity * are solids at room temperature, except for mercury (Hg), which is a liquid
Atoms and the Periodic Table / Metals, Nonmetals, and Metalloids
Nonmetals:
* are located on the right side of the periodic table
* usually do not have a shiny appearance
* are usually poor conductors of heat and electricity
* can be solids, liquids, or gases at room temperature solid liquid gas sulfur bromine nitrogen carbon oxygen
Nonmetals, and Metalloids
Metalloids:
* are located on the solid line that starts at boron (B) and angles down towards astatine (At)
* have properties intermediate between metals and nonmetals
* are represented by only seven elements:
boron (B) antimony (Sb) silicon (Si) tellurium (Te) germanium (Ge) astatine (At) arsenic (As) Atoms and the Periodic Table
Compounds
-Compound: a pure substance formed by chemically combining two or more elements together.
-A chemical formula consists of:
* element symbols to show the identity of the elements forming a compound
* subscripts to show the ratio of atoms in the compound
H2O C3H8
2 H atoms 1 O atom 3 C atoms 8 H atoms
Atoms and the Periodic Table / Compounds * Compounds can be drawn many ways:
* Different elements are represented by different colors:
Structure of the Atom
-All matter is composed of the same basic building blocks called atoms.
-Atoms are composed of three subatomic particles:
Structure of the Atom
Nucleus: Electron cloud:
-location of protons - location of electrons and neutrons -comprises most of the atom’s volume
-dense core of the atom
-location of most of the atom’s mass
Structure of the Atom / Atomic Number
From the periodic table:
3 Atomic number (Z) is the number of protons in the nucleus.
Li
* Every atom of a given element has the same atomic number. * Every atom of a given element has the same number of protons in the nucleus. * Different elements have different atomic numbers. * A neutral atom has no net overall charge, so Z = number of protons = number of electrons
Atomic Number and Mass Number * Atomic Number: equal to number of protons in each atom, which is equal to the number of electrons * Mass Number: number of protons plus number of neutrons
Isotopes / Isotopes, Atomic Number, and Mass Number * Isotopes are atoms of the same element that have a different number of neutrons. *
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