Atoms and Bonding Table of Contents Atoms Bonding

Atoms and Bonding Table of Contents Atoms, Bonding, and the Periodic Table Ionic Bonds Covalent Bonds Bonding in Metals

Elements • Element- A pure substance that cannot be broken down into any other substances by ordinary chemical or physical means – Elements are pure substances, composed of only one type of atom – Can be identified by specific chemical and physical properties – 92 elements occur naturally, the rest have been synthetically created in labs • Elements are often called the building blocks of matter because all matter is composed of one element or a combination of two or more elements

Atoms • Atoms- The smallest part of an element that has all the properties of that element • The basic particle from which all elements are made • The building blocks of matter • Made up of three main types of particles: • Protons- Positively charged particles located in the nucleus • Neutrons- Particles with no charge (neutral) found in the nucleus • Electrons- Negatively charged particles that whirl around in a cloudlike region beyond the nucleus of the atom

Molecules • Atoms of elements can chemically combine to form larger particles called molecules • Molecule- A combination of two or more atoms held together by chemical bonds – Represented by chemical formulas (ex. - water H 2 O) – Can be made of two or more of the same kind of atoms (ex. atmospheric oxygen O 2) – Can be made of different types of atoms (ex. - water H 2 O)

Compounds Compound- substance made of atoms of different elements that are chemically combined in a set ratio (ex. - table salt Na. Cl) – When elements are chemically combined, they form compounds having properties that are different from those of the uncombined elements – A compound may be represented by a chemical formula, which shows the elements in the compound and the ratio of the atoms – When atoms combine, only the electrons in the outermost energy shells combine This combining of elements to form new substances is called chemical bonding

Mixtures • Mixture- Matter that is made of two or more substanceselements, compounds, or both- that are together in the same place but are not chemically combined • Mixtures differ from compounds in two ways: – Each substance in a mixture keeps its individual properties – The parts of a mixture are not combined in a set ratio Components can be separated out by normal physical means

The Periodic Table • Periodic Table- A table in which the elements are arranged in order of increasing atomic number • The table has one square for each element • Each square lists the element’s name, chemical symbol, atomic number, and average atomic mass – Periodic Vocabulary: • Chemical Symbol- A one or two letter representation of an element • Atomic number- The number of protons in the nucleus of an atom • Average Atomic mass- The average mass of an atom for a particular element, based upon the number of protons and neutrons in the nucleus of an atom (based upon the combined percentages of all its isotopes)

Organizing the Periodic Table Properties of an element can be predicted from its location in the periodic table – Elements are placed in horizontal rows (called periods) based on atomic number • Atomic number increases across a period • Both the number of protons and the number of electrons increases by one as you move from one element to the next – Elements are placed in vertical columns (called groups or families) based on having the same number of electrons in their outermost energy shell which gives them similar chemical properties

Atoms, Bonding, and the Periodic Table Electron Dot Diagrams The valence electrons of an atom are shown as dots around the symbol of the element. Complete the electron dot diagram for neon. Valence electrons Electrons at higher energy levels that are involved in chemical bonding

Atoms, Bonding, and the Periodic Table 8 1 4 2 Periodic Table of the Elements The periodic table is arranged in order of increasing atomic number. The number of valence electrons also increases from left to right across a period. What is the number of valence electrons for each group?

Atoms, Bonding, and the Periodic Table The symbols for the elements in Periods 2 and 3 are shown below. Complete the electron dot diagrams for nitrogen, oxygen, fluorine, sodium, magnesium, aluminum, silicon, and argon.

Atoms, Bonding, and the Periodic Table Groups of Elements 1 High 7 High 8 Low

Ionic Bonds How Ions Form An atom that loses one of its electrons becomes a positively charged ion. The atom that gains the electron becomes a negatively charged ion.

Ionic Bonds Ions The table lists the names of some common ions, their charges, and their symbols.

Ionic Bonds Formation of an Ionic Bond Follow the steps to see how an ionic bond forms between a sodium atom and a chlorine atom. Complete the electron dot diagrams.

Ionic Bonds Halite Ions in ionic compounds are arranged in three-dimensional shapes called crystals. Some have a cubic shape.

Ionic Bonds Galena, or lead sulfide (Pb. S), has a structure similar to that of table salt.

Covalent Bonds Sharing Electrons By sharing 2 electrons in a covalent bond, each fluorine atom gains a stable set of 8 valence electrons. Which are the shared electrons that form a covalent bond between the 2 fluorine atoms?

Covalent Bonds Atoms can form single, double, and triple covalent bonds by sharing one or more pairs of electrons.

Covalent Bonds Nonpolar and Polar Bonds Hydrogen forms a nonpolar bond with another hydrogen atom. In hydrogen fluoride, fluorine attracts electrons more strongly than hydrogen does. The bond formed is polar.

Covalent Bonds Nonpolar and Polar Molecules Both carbon dioxide and water molecules contain polar bonds. Where would + and - signs be placed to show positive and negative charges?

Covalent Bonds Bonding Determines the Properties of a Substance Complete the information, using water and sodium chloride as examples. Water forms when two nonmetals (hydrogen and oxygen) share electrons Sodium chloride forms when positive and negative ions attract one another And when combined, the two make a mixture commonly known as saltwater

Bonding in Metals Metallic Bonding The positively charged metal ions are embedded in a “sea” of valence electrons.

Properties of Metals • The unique properties of metals result from the ability of their valence electrons to move about freely • Properties of metals include: • Luster- the way light reflects off the surface • Malleability- can be rolled into thin sheets • Ductility - can be bent easily • Thermal Conductivity- conduct heat easily • Electrical Conductivity- conduct electric current easily