Try This: NH4C2H3O2 Type of atom # of atoms N H C O Kesteyscience

Bonding

Valence Electrons Valence electrons are those electrons that are in the highest energy level (last energy shell) The number of valence electrons in an atom of an element determines many properties of that element, including the ways in which the atom can bond with other atoms

Electron Dot Diagrams An electron dot diagram includes the symbol for the element surrounded by dots. Each dot stands for one valence electron

Why do atoms bond together? We are going to use the term “Happy Atoms” Most atoms want to be happy! In order for atoms to be happy, their outer shells have to be full. Some atoms have too many electrons so they like to get rid of their extra electrons. Some atoms have a shell that’s really close to being full. So these atoms look for other atoms that are giving their extra electrons away. Look at the example on the screen. Sodium and Magnesium’s first two shells are completely filled. On their 3rd shells, there is a few extra electrons hanging out by themselves. What do we call these electrons? (VALENCE ELECTRONS). Sodium and Magnesium just want to be happy atoms! But right now, they aren’t happy. So Sodium and Magnesium have two options: 1. They can either fill up their 3rd shell completely with 8 electrons or 2. They can give away their extra electrons. What do you think is the easier option? (GIVE AWAY). Now they are on a hunt for an atom that has six or seven valence electrons to make them happy.

Oh Happy Day! Would you look at that! Here are Oxygen and Flourine looking to gain some electrons. Because they want to be happy atoms too! There are a few different ways that these atoms can get happy. They can share electrons, which makes a covalent bond. Or, they can just borrow the electrons, which makes an ionic bond. Let’s see what happens when we get these shells full.

When Sodium (red) gets together with Fluorine (blue), they both end up as happy atoms! Now, Sodium has a full outer shell and so foes fluorine. When an atom gives up an electron, it becomes positive. So which of the two elements will be positive? (Na+). When an atom gains an electron, it becomes negatively charged. Fl- The positive and negative charges attract to each other like magnets. The attraction of opposite charges is how atoms form and maintain (keep) the bond.

Why does bonding occur Atoms want to become stable

Have 8 valence and are very unreactive Stability Most atoms are more stable --- less likely to react---- when they have eight valence electrons. Have 8 valence and are very unreactive Some small atoms are stable with two valence electrons in their first and only row

Reaching stability In order for atoms to become stable they need to have a full outer energy level Atoms want to become an octet Octet-have 8 valence electrons Exception hydrogen and helium because the outer energy level is stable with two electrons

How many more electrons are need to make the following elements stable? P Al Be Mg S Cl

Atoms usually react in a way that makes each atom more stable One of two things can happen: The number of valence electrons increase to 8 The atom gives up loosely held valence electrons or Atoms that react this way become chemically combined- bonded to another atom

The Periodic Table The periodic table is a system used worldwide for organizing elements into categories. The way the elements are organized gives you important information about the arrangement of the electrons in their atoms

Periodic Table Gr oups As the number of protons (atomic number) increases, the number of electrons also increase As a result, the properties of the elements change in a regular way across a period A row of elements across the periodic table is called a period

How the Periodic Table Works As the number of protons (atomic number) increase, the number of electrons also increases The elements within a group have similar properties because they all have the same number of valence electrons in their atoms

Noble Gases Group 18 elements are known as the noble gases Atoms of these elements have 8 valence electrons- except for helium which has _______

As a result, noble gases do not react easily with other elements Remember when atoms get the maximum number of valence electrons---- 8 --- they become stable The variety of colors in a “neon” sign results from passing an electric current through sealed glass tubes containing different noble gases As a result, noble gases do not react easily with other elements

Now look at the elements in the column just to the left of the noble gases ----- Group 17 are called the Halogens

Halogens Atoms in the halogen family have ____ valence electrons A gain of just one more electron gives these atoms the stable number of 8 electrons As a result, elements in the halogen family react easily with other elements whose atoms can give up or share electrons

Atoms of alkali metals have only _____valence electron Group 1 is called the Alkali Metal Family Atoms of alkali metals have only _____valence electron except for lithium The energy level below this single electron contains a stable set of 8 electrons Has a stable set of two electrons in the energy level below the valence electron

Alkali metal can become chemically more stable by losing their 1 valence electron This property makes the alkali metals very reactive

(a halogen) reacts with aluminum, a purple gas is produced Elements in Group 17(the Halogens) and Group 1(the alkali metals) are highly reactive When iodine (a halogen) reacts with aluminum, a purple gas is produced Sodium (an alkali metal) reacts vigorously with bromine (a halogen)

Other Metals… Most have 1, 2, or 3 valence electrons Look at the elements in Group 2 through 12 Most have 1, 2, or 3 valence electrons They react by losing these electrons, especially when they combine with oxygen or one of the halogens

Other Metals How reactive a metal is depends on how easily its atoms lose valence electrons They react by losing these electrons, especially when they combine with oxygen or one of the halogens

Nonmetals combine with metals usually by gaining electrons But nonmetals can also combine with other nonmetals by SHARING electrons Of the nonmetals oxygen and the halogens are highly reactive In fact, FLOURINE is the most REACTIVE element known It even forms compounds with some of the noble gases

Metalloids Several elements known as metalloids lie along a zigzag line between the metals and nonmetals Quartz- movement watch keeps time with a small quartz crystal, a compound made of the metalloid silicon and the nonmetal oxygen The metalloids have from 3 to 6 valence electrons and can either lose or share electrons when they combine with other elements

Hydrogen Hydrogen is considered to be a nonmetal It is located above Group 1 in the periodic table because it has only one valence electron However, even though hydrogen is a reactive element, its properties differ greatly from those of the alkali metals