Chapter 7: Atoms and Molecules

Chemistry Chemistry is the study of matter and how matter interacts with each other Matter is made up of small particles called atoms An atom is the smallest part of matter/an element that can be recognized as that element

Atoms Atoms are made of three particles Nucleus- condensed center of an atom 1. Protons- positively charged particles inside the nucleus of an atom 2. Neutrons- neutral/no charge particles inside the nucleus of an atom Shells- space surrounding the nucleus of an atom 3. Electron- negatively charged particles travelling around the nucleus of an atom

Atomic Number The atomic number is the number that represents the element- it is the number of protons in a given atom/element Niels Bohr- developed the Bohr model of an atom that simplifies the structure of an atom

Atomic Theory Describes how scientists think about atoms It states that all matter is made of atoms and that each element has its own characteristics based on the number of particles in it, also reactions occur when these atoms of given elements are rearranged

Elements Classifying Elements Chemical symbols- are abbreviations for the names of the elements The first letter of a chemical symbol is always a capital letter The second (and third) letter (s) are always lower case A capital letter always indicates a new element CO= Carbon and Oxygen – Carbon monoxide, a gas Co= Cobalt, a metal

Periodic Table of Elements Dimitri Mendeleev is the chemist responsible for creating the Periodic Table of Elements (POE) Elements were arranged by atomic weights and space was left for the possible discovery of new elements The current POE arranges the elements by atomic number (number of protons) and space is still left for possible new elements

Periodic Table of Elements Elements are arranged on the POE in both horizontal rows and vertical columns Periods- horizontal rows- have some similarities Groups- vertical columns Each element in a group has the same number of electrons in the outermost shell The elements are also classified on the POE by categories called families- based on similar properties shared by all elements in that family

Periodic Table of Elements Families Alkali Metals Alkaline Earth Metals Transition Metals Inner Transition Metals Semi-metals or Metalloids Nonmetals

Compounds When atoms join together with other atoms to form units they are called molecules The process of combining different types of atoms is called a chemical change or chemical reaction Compounds- are the products of chemical changes A combination of 2 or more different atoms types of elements

Common Compounds H2O- water NaCl- sodium chloride- table salt

Chemical Formulas Chemical formulas are symbols and numbers used to abbreviate the name and number of elements/atoms in a compound It tells you how the atoms of elements combine and what the compound is C6H12O6 Table sugar There are 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms for every sugar molecule

Chemical Reactions Chemical reactions occur between the electrons of atoms There are several different types of reactions Synthesis- elements combine Decomposition- compounds break down Single replacement- one element replaces another Double replacement- two elements switch places

Chemical Reactions Synthesis- elements combine Decomposition- compounds break down Single replacement- one element replaces another Double replacement- two elements switch places

Quick Check p 169 What is a chemical reaction? Which two substances join to make carbonic acid? Is carbonic acid a different substance than carbon dioxide and water? What is this type of chemical reaction called?

Quick Check p 169 What is a chemical reaction? The process through which different types of atoms join together Which two substances join to make carbonic acid? Carbon dioxide and water Is carbonic acid a different substance than carbon dioxide and water? Yes What is this type of chemical reaction called? Synthesis reaction

Atomic Bonding Atoms will bond with each other depending on the number of electrons in their outermost shell. Each shell can only hold a certain number of electrons and once that is filled the shell is closed and “stable”

Covalent Bonds This occurs when atoms share their electrons in pairs This sharing allows each atom to have the number of electrons they each need to be stable This occurs most often in gases and liquids; although it can occur, rarely, in metals O2 and H2O are both examples of covalent bonding

Ionic Bonding Occurs when an electron is transferred from one element to another When an atom has lost or gained an electron it is called an ion This is when the number of electrons does not equal the number of protons in the atom’s nucleus If they lose electrons and there are more protons than electrons it is positive ion (cation) If they gain electrons and there are more electrons than protons it is a negative ion (anion)

Ionic Bonding When a negative and positive ion are near each other they are attracted to each other and join together Opposites attract! This forms and ionic bond

Acids and Bases: Acids Acids form hydrogen ions (H+) when they are dissolved in water Their strength depends on how many hydrogen ions form They can be corrosive- able to dissolve metal (i.e. hydrochloric acid) Examples are lemon juice, vinegar and of course stomach acid They have a pH of 0-6.9

Acids and Bases: Bases Bases form hydroxide ions (OH-) when dissolved in water The strength of a base depends on how many hydroxide ions form They have a pH of 7.1-14 Some are weak and some are strong Some examples include baking soda and antacids If a base dissolves in water it is called alkali

Acids and Bases: pH Scale The pH scale means “power” or “potential” of “hydrogen” (puissance de l'hydrogène) It is a measurement of acidity or alkalinity (bases) 0-6.9 is an acid 7.0 is neutral- neither an acid nor a base 7.1-14 is a base

Acids and Bases: Indicators Acids and bases are usually found in water solutions An indicator is a substance that will change color when exposed to an acid or a base Litmus paper is an indictor Blue litmus changes to red in an acid and has no change in a base Red litmus changes to blue in a base and has no change in an acid

Acids and Bases: Neutralizing Acids and Bases When an acid and a base come in contact with each other they will neutralize or cancel each other out An acid will neutralize a base when it is of equal strength and a base will neutralize an acid the same way When acids and bases come in contact with each other they form salts A salt is an ionic compound that contains positive ions from a base and negative ions from an acid Most are made of a metal and a non-metal