Chemistry of Atoms Chapter 4

Weekly Objectives All organisms are made of cells, and all cells are made of chemical substances, including water, carbohydrates, proteins, and fats. Water is one of the most important substances for life. In Chapter 2, you will learn what living things are made of, what your body is made of, what cells need to function, and how energy is important to you. You will also learn about the chemical properties of substances that are essential for life. Section 1  Identify the components of atoms  Differentiate between atoms and elements  Distinguish between bond types

The Nature of Life reference pp. 28 All matter is made of atoms. An atom is the smallest unit of matter that can not be broken down by chemical means.

What Makes Up An Atom? Atoms have 3 main parts (subatomic particles) PartLocationCharge ProtonInside the nucleus of the atom Positive charge (represented using a + sign) ElectronSurrounds the nucleus of the atom (Are in constant motion) Negative charge (represented using a – sign) NeutronInside the nucleus of the atom Have a neutral charge

HELIUM ATOM + N N proton electron neutron Shell What do these particles consist of? Proton Neutron Electron Shell Electron

What is an element? An element is considered a pure substance because it is made of only one kind of atom. There are more than 100 different known elements. Each element is represented by a one-, two-, or three-letter symbol. Example: He- helium, Ar-argon, Au-gold An atom of the same element with a different number of neutrons is called an isotope. Where can we find a collection of elements?

The Periodic Table The periodic table is a collection of elements in rows and columns, highlighting the regular repetition of properties of the elements The table gives valuable information which includes Atomic Number Atomic Mass Atomic Symbol

When Atoms Combine The goal of every atom is to become stable This can be achieved by creating bonds with other elements to completely fill outer electron shells Atoms that are unstable—that is, atoms in which the outer electron level is not full—will react readily with atoms that can fill their outer electron level. When two or more atoms of different elements form chemical bonds with one another, the joined atoms form a stable substance called a compound.

Electron Shell/ Maximum # of Electrons  Shell 1= 2  Shell 2= 8  Shell 3= 18  Shell 4= 32  Shell 5= 50  Shell 6= 72

Describing Atoms  Atomic Number = number of protons and electrons  In a neutral atom, the # of protons = the # of electrons  Atomic Mass= sum number of protons + the number of neutrons

Ions  An atom that carries an electrical charge is called an ion  If the atom loses electrons, the atom becomes positively charged (because the number of positively charged protons will be more the number of electrons)  If the atom gains electrons, the atom becomes negatively charged (because there are more negative charges than positive)

Ions  The number of protons does not change in an ion.  The number of neutrons does not change in an ion.  So, both the atomic number and the atomic mass remain the same.

Ions This atom has lost an electron. Now it has one more proton than electron. One more proton means one more positive charge. This makes the total charge of the atom POSITIVE. This atom has gained an electron. Now it has one less proton than electron. One less proton means one less positive charge. This makes the total charge of the atom NEGATIVE.

Isotopes  The number of protons for a given atom never changes.  The number of neutrons can change.  Two atoms with different numbers of neutrons are called isotopes  Isotopes have the same atomic #  Isotopes have different atomic Mass # ’ s

Types of Bonds  Covalent Bonds- when atoms share electrons  Ionic Bonds – when atoms give or take electrons  Hydrogen Bonds- a covalent bond develop strictly between hydrogen atoms

Covalent Bond

Ionic Bond

Hydrogen Bond Because water molecules have a unequal distribution of electrical charge, it is considered to be polar. When compounds have equal charges it is considered nonpolar.