5-1 Notes - Compounds Chapter 5, Lesson 1

Compounds A compound is a pure substance that contains two or more different elements. CO2 H2O HCl O2

Compounds A chemical formula is an ingredient list for a compound that uses symbols and subscripts.

Compounds formula – shows the ratio of elements in a molecule formulas of familiar compounds: Compound Formula Water H2O Carbon Dioxide CO2 Carbon Monoxide CO Methane CH4 Ammonia NH3 Table Sugar C12H22O11 formula – shows the ratio of elements in a molecule subscript – shows the number of atoms of an element in a molecule

Compounds sucrose (sugar) C12H22O11

Compounds and Elements A compound has different properties than the elements that make it up. The element Sodium (Na) is a soft metal and is DANGEROUS by itself. The element Chlorine (Cl) is a greenish-yellow gas and is DEADLY by itself. The compound Sodium chloride (NaCl) is table salt and you eat it all the time!

Lewis Dot Diagrams The force that holds atoms together in a compound is called a chemical bond. caffeine

Lewis Dot Diagrams The electrons in an atom’s outside energy level are called valence electrons.

Lewis Dot Diagrams Valence electrons are the only ones involved in forming bonds. GROUP NUMBER VALENCE NUMBER

Lewis Dot Diagrams Lewis dot diagrams use symbols and dots to represent the valence electrons. 1A 2A 3A 4A 5A 6A 7A 8A

Lewis Dot Diagrams

Ionic Compounds An ionic compound is when two or more elements or compounds gain or lose electrons and form ionic bonds.

Ionic Compounds An ionic bond is an electrical attraction between positively and negatively charged ions. Cl- Na+

Another casualty in the War of the Atoms

Ionic Compounds An atom can become charged by giving one or more electrons to another atom. Both atoms become ions.

Ionic Compounds The positive ion is usually a metal (Lithium) The negative ion is usually a non-metal (Fluorine) positive ions negative ions

Ionic Compounds Lithium loses its 1 valence electron and becomes a positively charged ion (1+). Fluorine gains the 1 valence electron and becomes a negatively charged ion (1-).

Ionic Compounds The lithium ion (1+) and fluorine ion (1-) now have equal and opposite charges. They are attracted to each other and form a compound: Lithium fluoride (LiF).

Ionic Compounds Lithium fluoride is made only of 2 elements and known as a binary compound.

Ionic Compounds 1 1A 17 7A Elements in the same column on the periodic table form a group.

Ionic Compounds 1 1A 17 7A Atoms in Group 1 (1A) give up 1 electron to become 1+ ions. 1+

Ionic Compounds 1 1A 17 7A Atoms in Group 17 (7A) need 1 electron and form 1- ions. 1-

Ionic Compounds 1 1A 17 7A When a positive ion from Group 1 and a negative ion from Group 17 combine, a salt such as sodium chloride (NaCl) forms.

Ionic Compounds 2 2A 16 6A Group 2 (2A) elements give up 2 electrons to form ions with a 2+ charge. Group 16 (6A) elements need 2 electrons and form ions with a 2- charge.

Ionic Compound Properties Usually solids at room temperature Brittle and break apart easily Have high melting and boiling points Many dissolve in water and become good conductors of electricity (saltwater)

Noble Gases Elements in Group 18 are the noble gases. Noble gases are stable because their outer energy levels are filled. Stable elements rarely react to form compounds.

Gain Electrons to be Noble Gas Chlorine can achieve noble gas structure by filling its outer energy levels. Chlorine can become more stable by gaining one electron and forming the Chloride ion Cl–.

Gain Electrons to be Noble Gas Chlorine WANTS to be just like Argon, the Noble Gas in its row.

Lose Electrons to be Noble Gas Magnesium can achieve the electron structure of Neon, the nearest noble gas on the periodic table. Magnesium can lose two electrons to form the stable ion Mg2+.

Lose Electrons to be Noble Gas Magnesium WANTS to be just like Neon, the Noble Gas in its row.

Covalent Compounds If an element needs to gain or lose too many electrons, it shares instead. A covalent bond is a chemical bond formed when atoms share electrons.

Covalent Compounds Carbon has 4 valence electrons. Too much energy is needed for carbon to easily gain or lose 4 electrons, so it shares.

Covalent Compounds Elements that are close together on the periodic table are more likely to share electrons in a covalent bond than to transfer electrons (or atoms bonding with themselves).

Covalent Compounds All organic compounds are covalent compounds based on carbon atoms.

Covalent Compounds

Ionic Compounds

Covalent Compound Properties Can be solids, liquids, or gases at room temperature Usually have lower melting and boiling points than ionic compounds Do not usually separate in water Most do not conduct electricity (sugar water) Is called a molecule - a neutral particle that forms as a result of electron sharing

Covalent Compound Properties The number of bonds an atom can form = the number of valence electrons needed to make a total of 8.

Covalent Compound Properties H needs 1 valence electron, so it can make 1 bond. C needs 4 valence electrons, so it can make 4 bonds. N needs 3 valence electrons, so it can make 3 bonds.

Multiple Bonds Covalent bonds can consist of: Single bonds (one pair of electrons shared) Double bonds (two pairs of electrons shared - stronger than single bonds) Triple bonds (three pairs of electrons shared - stronger than double bonds).

Multiple Bonds The shared pair of electrons is a single covalent bond, which holds the hydrogen molecule H2 together.

Fail.

5.1 How Atoms Form Compounds Bromine is in Group 17. How many electrons does bromine need to gain or lose to obtain a noble gas structure? A gain one electron B gain two electrons C lose one electron D lose two electrons

Which element can form a negative ion? A carbon B magnesium C chlorine 5.1 How Atoms Form Compounds Which element can form a negative ion? A carbon B magnesium C chlorine D lithium

What holds two elements together in an ionic bond? 5.1 How Atoms Form Compounds What holds two elements together in an ionic bond? A covalent bonds from shared electrons B electron clouds combining C unpaired electrons attracting each other D opposite charges on negative and positive ions

How many dots are in a Lewis dot diagram for the Group 1 element lithium? B 2 C 3 D 4

Why are noble gases unlikely to form compounds with other elements? A They form ionic bonds. B They have 8 valence electrons. C They form covalent bonds. D Their outer energy levels are not filled with electrons.

Compounds sharing electrons are held together by ____. A ionic bonds B covalent bonds C metallic bonds D polymer chains

Which elements are least likely to react with other elements? A metals SCI 3.b Which elements are least likely to react with other elements? A metals B Group 17 elements C Group 16 elements D Noble gases

SCI 3.b In the ionic compound magnesium oxide (MgO), how many electrons did oxygen give magnesium? A 1 B 2 C 3 D none of the above

Noble gases are in which group on the periodic table? A 1 B 2 C 17 SCI 3.f Noble gases are in which group on the periodic table? A 1 B 2 C 17 D 18

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