Chapter 1: Chemical Bonds Chemistry Chapter 1: Chemical Bonds

Vocab Electron cloud Energy levels Periodic Table Electron dot diagram Chemical bond

Atom Structure Everything is made up of atoms At the center of every atom is a nucleus containing protons (+ charge) and neutrons (no charge) The nucleus represents most of the atom’s space The rest of the atom’s space is empty except for the atom’s electrons (- charge) which travel in an area of space around the nucleus called the electron cloud

Electrons Electrons have negative charges Electrons travel in predictable areas (electron clouds) but not predictable patterns

Element Structure Each element has a different atomic structure made up of a specific number of protons, electrons, and neutrons The number of protons and electrons is always the same for a neutral element

Electron Arrangement The number and arrangement of electrons in the electron cloud are responsible for many of the chemical and physical properties of that element.

Electron Energy All electrons in an atom are in the electron cloud but some electrons are closer to the nucleus than others Energy levels: The different positions of electrons in an atom Each level represents a different amount of energy

Number of Electrons Each energy level can hold a specific number of electrons The farther away an energy level is from the nucleus the more electrons it can hold Ex. The first can hold 2, the second up to 8, and the third up to 18 electrons

Second Energy Level First Energy Level

Energy Steps A stairway is an excellent model to show the maximum number of electrons each energy level can hold in the electron cloud. Electrons nearest the nucleus have the lowest amounts of energy and are the hardest to remove Electrons farthest from the nucleus have the most amounts of energy and are the easiest to remove

Energy Steps

Ex. Picture a magnet with a chain of paperclips hanging off of it. The easiest paperclip to remove is the one at the very end of the chain because the pull of the magnet isn’t as strong Hardest to remove Easiest to remove

Periodic Table and Energy Levels Periodic Table: A way of representing all of the elements in a way that shows their similarities and differences First discovered by Dmitri Mendeleev in 1869 Horizontal rows are called periods Vertical columns are called groups or families The atomic number is the same as the number of protons and electrons Today’s periodic table is still based on the one I created almost 140 years ago!

Reading the Periodic Table

Electron Configuration The number of electrons in a neutral atom increases from left to right across a period Atoms whose outer energy levels contain one of the levels in the stair step analogy are considered stable Each period ends with a stable element

Element Families Each column of the Periodic Table contains one family Hydrogen is considered separate from the rest of the families Just like human families, element families have similar traits (chemical properties) Mendeleev was inspired by the repeating patterns he heard in music and saw similar repeating patterns in the elements

Noble Gases Made up of the elements in Group 18 Helium, Neon, Argon, Krypton, Xenon, Radon All are stable and have 8 electrons in their outer energy levels At one time these gases were thought to be inert (non reactive) but this was later found to be untrue and the name changed to the Noble gases Used to protect filaments in light bulbs and produce colored light in signs

Halogens Made up of the elements in Group 17 Fluorine, Chlorine, Bromine, Iodine, Astatine Unstable – Halogens need one electron to obtain a stable outer energy level The easier it is for a Halogen to form a bond, the more reactive it is Fluorine is the most reactive because its outer energy level is closest to the nucleus Used to disinfect drinking water, in clothing bleach, production of paper, and removal of germs during sterilization

Alkali Metals Made up of the elements in Group 1 Lithium, Sodium, Potassium, Rubidium, Caesium, Francium (Hydrogen is not included) Unstable - have one electron in their outer energy level  Highly reactive Used to create flavorings and preservatives and in the manufacturing of paper, soap, and ceramics

Electron Dot Diagrams Electron dot diagram: a diagram that shows the number of electrons in the outer energy level Valance Electrons: electrons in the outer energy level Helpful in determining the chemical properties of an atom and when showing how atoms bond Also called Lewis Structures Created by Gilbert N. Lewis

How to Write Them For groups 1, 2 and 13-18 see pg. 11 in your book. Dots are written in pairs on the four sides of the element symbol The dots are written in this order 1 5 Ne 4 6 8 2 3 7

Using Dot Diagrams Can be used to show how atoms bond with each other Chemical Bond: the force that holds two atoms together Atoms bond with each other in a way that makes them become more stable by filling up their outer energy levels

Section 2: How Elements Bond

Vocab Ion Ionic bond Compound Covalent bond Metallic bond Molecule Polar bond Chemical formula

How Elements Bond When atoms are joined together they do not fall apart easily Atoms form bonds with other atoms using the electrons in their outer energy level There are 4 ways this can be done: Losing electrons Gaining electrons Pooling electrons Sharing electrons

Ionic Bonds – Loss and Gain Occurs between metals and nonmetals Atoms gain and lose electrons to form bonds

Ions – A Question of Balance Atoms lose or gain electrons and become more stable When an electron is lost, the electric charge changes because there is now one more proton than neutron in the nucleus and it is called a positive ion When an electron is gained you create a negative ion Ion: an atom that is no longer neutral because it has lost or gained an electron

Examples of ions: Sodium loses one electron to become a Na+ ion Chlorine gains one electron to become a Cl- ion

Bond Formation Negatively charged ions and positively charged ions are attracted to each other Ionic Bond: attraction that holds oppositely charged ions together Ex. Sodium (Na) loses an electron and becomes a positive ion. Chlorine (Cl) gains an electron from Sodium (Na) and becomes a negative ion. The two ions are attracted together by an ionic bond

Pure substances are divided into two categories: Element: cannot be separated into any simpler substances Ex. Sodium and Chlorine Compound: a substance containing two or more elements that are chemically bonded Ex. Sodium Chloride

More Gains and Loses Some atoms need to lose/gain more than two electrons to become stable Atoms can do this by bonding to another atom that needs to gain/lose as many electrons as they need to lose/gain or by bonding to more than 1 atom

Ex: Magnesium needs to lose 2 electrons Oxygen needs to gain 2 electrons The 2 in the superscript represents the number of electrons that were gained/lost If only one electron is gained or lost no number is needed in the superscript

Ex: Magnesium needs to lose 2 electrons 2 Chlorine atoms that each need to gain 1 electron

Metallic Bonding - Pooling Occurs between two metals Metallic Bonding: Metal atoms pool their electrons to form bonds In metals, electrons are not held tightly to the individual atoms. Instead they move freely among all the atoms in the metal forming a shared pool of electrons This is why metal can be hammered into sheets without breaking and is a good conductor of electricity

Covalent Bonds - Sharing Occurs between 2 nonmetals Some atoms need to gain/lose too many electrons (this needs too much energy) to create ionic bonds Instead two nonmetals share their electrons Covalent Bond: chemical bond that forms between the shared electrons Electrons are attracted to the nuclei of both atoms and move back and forth between them Molecule: neutral particle formed in a covalent bond

Ex. Two chlorine atoms form a stable molecule by sharing electrons to fill their outer energy level

Double and Triple Bonds Sometimes an atom shares more than one electron with another atom When two pairs of electrons are shared it is called a double bond When three pairs of electrons are shared it is called a triple bond

Polar and Nonpolar Molecules While atoms share electrons to become stable they do not always share electrons equally Some atoms have a stronger attraction to electrons than others This unequal sharing makes one side of the bond more negative than the other Polar bond: bond where the electrons are shared unevenly Ex. Water molecules Nonpolar bonds: bond where electrons are shared evenly

The Polar Water Molecule 2 hydrogen atoms and 1 oxygen atom bond together in a covalent bond The oxygen has a greater share of the electrons (sharing one electron with each hydrogen) The oxygen end has a negative charge The hydrogen has a positive charge

Chemical Shorthand In medieval times alchemists were the first to explore the world of chemistry They believed in magic and mythical transformations Discovered many properties of the elements Created many symbols to represent the elements Many are still used today Alchemists, like me, were mainly concerned with transforming ordinary metals into gold

Symbols for Atoms Modern chemists use symbols to represent atoms These symbols can be understood by chemists all over the world Each element is represented by a one or two letter symbol Many symbols are created by using the common name of the element Ex. H for Hydrogen Some symbols are creating by using the name of the element in another language Ex. K for Potassium (which is called Kalium in Latin)

Symbols for Compounds Compounds can be described using element symbols and numbers Ex. H2 This tells us that there are 2 Hydrogen atoms in this molecule

Chemical Formulas Chemical Formula: combination of chemical symbols and numbers which shows which elements are present in a compound Ex. Ammonia or NH3 This tells you that the ratio is one nitrogen atom to three hydrogen atoms