Chapter 3

Elements, Atoms, and Ions

Alchemy - pseudoscience based upon thebelief that cheap metal could be turned intogold

Greek philosopher Aristotle proposed that allmatter is made up of a combination of fourbasic elements:

Air, water, fire, earth

There are 115 known elements, of those 92 occur naturally in the universe. The rest are man-made.

Each element has a chemical symbol. The symbols come from:

-the first letter of the name of the element-the first letter and one other letter in the name-the Greek or Latin name for the element.

Only the first letter of the symbol is capitalized.

3.3 Dalton’s Atomic Theory3.3 Dalton’s Atomic Theory

Law of Constant Composition

A given compound always contains the same proportions by mass of the elements.

John Dalton - English scientist who proposedthat matter is made up of atoms

Dalton’s Atomic Theory

1. All matter is made up of tiny particles calledatoms.

2. All atoms of a given element are identical in mass and properties.

4. When elements react, their atoms combine in simple, whole-number ratios.

3. Atoms of a given element are different from those of any other element.

5. Atoms are indivisible and indestructible in chemical processes.

chemical formula - shows the types of atomsand the number of each type in a molecule ofa given compound

* Rules for Writing Formulas, p. 54.

History of the AtomHistory of the Atom

J.J. Thomson - showed that atoms of any element can be made to emit negative particles.

He concluded that all atoms must contain the negative particles we now call electrons.

He also concluded that atoms must containpositively charged particles to balance out thenegative charges of the electrons.

William Thomson (aka Lord Kelvin)-proposed that an atom might be like a plum pudding-believed the electrons were randomly scattered throughout a uniform “pudding” of positive charge

Ernest Rutherford’s Gold Foil ExperimentRutherford aimed a beam of alpha particles ata sheet of gold foil. Most of the particles wentstraight through the foil, but some were deflectedat large angles or even backward.

He concluded: 1.Atoms contain a dense center or nucleus of

positive charge around which electrons move.2. Atoms are mostly empty space. He later concluded that the nucleus must contain protons or positively charged particlesto balance out the negative electrons.

An atom consists of a tiny nucleus and electronsthat orbit around the nucleus.

The nucleus contains:protonsneutrons

- positively charged- no charge

Electrons have very little mass, so the mass of an atom comes from the protons and neutronsin the nucleus.The properties of an element are due to thenumber and arrangement of electrons in its atoms.

Atoms have an equal number of electrons andprotons.

The number of protons in the nucleus of an atom is called the _______________.atomic number

The sum of an atom’s protons and neutrons iscalled the ________________.mass number

Atoms of the same element with different numbers of neutrons are called ____________.isotopes

Copyright © Houghton Mifflin Company 3-17

Figure 3.11:Figure 3.11: The periodic table The periodic table

http://bstacy1.edu.glogster.com/history-of-the-periodic-table/

Elements are listed on the periodic table inorder of increasing _________________. atomic numbers

Dmitri Mendeleev - 1869, arranged the knownelements according to increasing atomic mass

He found that the elements could be grouped together into vertical families with similar properties.There were some inconsistencies with hisarrangement.

Henry Moseley - 1913, arranged the elements according to increasing atomic numbers

Prior to Moseley, atomicnumbers were thought of asarbitrary numbers. He showed that they were notarbitrary, but had anexperimentally measurablebasis.

Modern Periodic Law“The properties of elements are a periodicfunction of their increasing atomic numbers.”Horizontal rows on the periodic table are called __________.periods

Vertical columns are called families or ________.groups

Elements in the same family have similar chemical properties.

The period number is called the principle quantum number and it represents the numberof electron energy levels of the elements in that period.

Alkali Metals- Group 1- very reactive metals

Alkaline Earth Metals- Group 2

Halogens- Group 7- very reactive nonmetals

Noble Gases- Group 8- nonreactive gases

Transition Metals - group of metals betweenGroups 2 and 3

Element Song

Hydrogen - most common element in the universe

- behaves like no other element- very reactive with other elements

Metals- good conductors of heat and electricity- malleable- ductile- shiny

Nonmetals- nonconductors- dull, brittle

Metalloids- elements located along the “stair-step”- have both metallic and nonmetallic properties

Very few elements exist in nature in their pureuncombined form.Gold, silver, and platinum are called ___________because they are relatively unreactive. noble metals

Many elements exist in the form of diatomicmolecules: molecules made up of two atoms.

Metals are solid at room temperature.Many nonmetals are solid and many are gases at room temperature.Only two elements are liquid at room temperature:

mercury (Hg) and bromine (Br2)

Different forms of a given element are called___________.allotropes

Carbon has three allotropes:DiamondGraphiteBuckminsterfullerene

Ion - an atom or group of atoms that has gained or lost electrons

Cation - positively charged ion- formed when an atom loses one or more electrons- named using the name of the parent atom

Example: A sodium atom will lose one electronto become a sodium ion (Na+).

Anion - negatively charged ion- formed when an atom gains one or more electrons- named by taking the root name of the atom and changing the ending to - ide.Example: A chlorine atom will gain one electron to become a chloride ion (Cl-).

All alkali metals (Group 1) form 1+ ions.All alkaline earth metals (Group 2) form 2+ ions.All Group 3 metals form 3+ ions.All Group 6 nonmetals form 2- ions.All halogens (Group 7) form 1- ions.

Ionic compounds - compounds formed due to the attraction between metal cations and nonmetal anions

Example: sodium chloride, NaCl

The Na+ and Cl- are attracted to each otherand held together by the opposite charges.

Ionic compounds can conduct electric current.

* Example 3.6, p. 77.

Ionic compounds are also called salts.

A chemical compound must have a net chargeof zero. For an ionic compound:

total positivecharge ofcations

total negativecharge of

anions+ = zero net charge

Na+ + Cl- NaCl

Ionic compounds are also called salts.