Essay

Atoms and the Periodic Table

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. *