Unit 2 Chemistry and Radioactivity Chapter 4: Atomic theory explains the formation of compounds

Chemistry Learning Outcomes Differentiate between atoms, ions and molecules using knowledge of their structure and components. Classify substances as acids, bases or salts based on their characteristics, name and formula. Distinguish between organic and inorganic compounds. Analyze chemical reactions, including reference to conservation of mass and rate of reaction. Explain radioactivity using modern atomic theory.

Words to Know: Chapter 4.1 Atomic Theory and Bonding, pages 168 -183 of BC Science 10 Textbook Words to Know: atomic number Bohr diagram compound covalent bonding ionic bonding ions Lewis diagram molecule valence electrons

What is an Atom? The smallest particle of an element that still has the properties of that element Fun Fact: 50 million atoms, lined up end-to-end = 1 cm How small is an atom? https://www.ted.com/talks/just_how_small_is_an_atom An atom = proton(s) + electron(s) + neutron(s) (PEN)

How small is an atom? https://www.ted.com/talks/just_how_small_is_an_atom

Pure Substances: Are substances that are made of only one kind of matter. Eg. Iron , Oxygen, Hydrogen 1

Pure Substances can be classified as either: ELEMENTs – pure substance that cannot be chemically broken down into simple substances are made up of one type of atom Eg. oxygen, Eg. hydrogen 2. COMPOUNDS – pure substances made up of more than one type of atom that are chemically combined. eg. H2O is a compound

Physical Change Is a change when the substance retains its original properties. Eg. a cut strawberry is still as sweet 1. Change in shape – bending, cutting 2. Dissolving: when salt dissolves in water, the crystals disappear but the salty taste of water proves that the salt is still there. The salt can be re-crystallized by evaporating the water. 3. Change of state (phase change): water boiling to steam

Chemical Change: occurs when the arrangement of atoms in compounds change, resulting in a new compound being formed. The change is irreversible Evidence of a new substance: Gas produced (bubbles) New change in colour, odour Energy (heat or light) release or absorbed Evidence of a chemical change: new substance created indicated by change in smell, color, temperature, production of a gas.

Structure of an Atom: The nucleus is at the centre of an atom protons (positive charge) and neutrons (neutral charge), both found in the nucleus Electrons (negative charge) exist in the space surrounding the nucleus

Subatomic particles have mass

Atomic number = # protons Atomic Mass = protons + neutrons

Where does most of the atom’s mass exist? Nucleus (protons and neutrons)

What makes up most of the atom’s volume? electrons

Question What determines the nuclear charge? Protons – bc neutrons are neutron and electrons are outside

Question Which particles determine the atomic number? Protons and electrons

Question Which particles determine the atomic number? Protons (or electrons) Protons and electrons

Numbers to Remember : Atoms are neutral, therefore: # of protons = # of electrons in every atom AND ONLY IN ATOMS!!! (not ions) Nuclear charge = charge on the nucleus = # of protons Atomic number = # of protons = # of electrons Why does nuclear change only depend on protons? Electrons are outside and neutrons are neutroal

Does atomic mass always equal atomic number?

Is atomic mass always twice the atomic number? Does atomic mass always equal atomic number?

Homework Read pages 168-171 Answer Check your Understanding: p183 #1-3, 5-9, 10f, 11 Read pages 174-177 in text book

Video Crash Course periodic table: https://www.youtube.com/watch?v=0RRVV4Diomg&list=PL8dPuuaLjXtPHzzYuWy6fYEaX9mQQ8oGr&index=4 Crash Course periodic table: https://www.youtube.com/watch?v=0RRVV4Diomg&list=PL8dPuuaLjXtPHzzYuWy6fYEaX9mQQ8oGr&index=4

The Periodic Table: The periodic table organizes the elements by atomic number There are 3 types of elements: metals are on the left non-metals are on the right metalloids form a “staircase” in the middle. Rows of elements (across) are called periods Columns (vertical) are called groups/families

Families of the Periodic Table: All elements in a family have… similar properties bond with other elements in similar ways have the same number of valence electrons Family names: Group 1 = alkali metals (sodium) Group 2 = alkaline earth metals (calcium) Group 17 = the halogens (chlorine) Group 18 = noble gases (neon) First column (Group 1) of Periodic Table (but does not include Hydrogen. They all have one electron in their outer shell. Metallic elements that are shiny, soft and have low densities. Malleable (bendable), some soft enough can be cut with a knife Not found freely in nature because they all react vigorously with oxygen and water Second most reactive family When mixed in solution they are likely to form “basic” or “alkaline” solutions. 2 electrons in valence shell

Group I: Alkali Metals does not include Hydrogen. all have one electron in their outer shell. Metallic elements that are shiny, soft and have low densities. Malleable (bendable), some soft enough can be cut with a knife Not found freely in nature because they all react vigorously with oxygen and water

Group II: Alkali Earth Metals Second most reactive family When mixed in solution they are likely to form “basic” or “alkaline” solutions. 2 electrons in valence shell

Group XVII: Halogens Non-metals seven electrons in their outer shell very reactive Greek words meaning “forming salts.” Fluorine most reactive. halogens are often used to kill harmful microorganisms. For example, the halogen chlorine is used to prevent the growth of algae in swimming pools and to purify drinking water. Solutions containing iodine are often used in hospitals and in doctors’ offices to kill germs on skin.

Group XVIII: Nobel Gases Have eight electrons in their outermost orbitals. Inert (non-reactive) The noble gases and helium are all "happy," because their valence shell is full.  Helium (He) is different from all of the other elements. It is very stable with only two electrons in its outer orbital (valence shell). Even though it only has two, it is still grouped with the noble gases

Where are the following? INCREASING REACTIVITY Where are the following? Atomic Number Period Group/Family Metals Non-metals Transition metals Metalloids Alkali metals Alkaline earth metals Halogens Noble gases rows of elements called periods. vertical columns of elements are called groups, or families.

Bohr Diagrams Show the arrangement of subatomic particles in atoms and ions. Electrons arranged in energy levels called shells. First shell contains 2 electrons, then 8, 8, 18, 18. Outermost shell is called valence shell. Stable octet is when the valence shell has 8 electrons.

Bohr Diagram

What patterns do you notice? Within a row? Within a family? What patterns do you notice (period row – shell, and group/columne and valence e)

What patterns do you notice (period row – shell, and group/columne and valence e) Note: The noble gas elements have full electron shells, and are very stable.

Row determines # shells Except for the transition elements,

Group number (column) determines the number of valence electrons

Bohr Diagrams: Practice What element is this? It has 2 + 8 + 8 = 18 electrons, and therefore 18 protons It has 3 electron shells, so it is in period 3 It has 8 electrons in the outer (valence) shell 18 p 22 n Argon

Ions It is more stable to achieve a full valence shell (like the noble gases). To do this, atoms will either lose or gain electrons to become ions (electrically charged particles)

What does sodium need to do to become more like a noble gas? Chlorine? Note: The noble gas elements have full electron shells, and are very stable. What does sodium need to do to become more like a noble gas? Chlorine? Note: The noble gas elements have full electron shells, and are very stable. What does sodium need to do to become more like a noble gas? Chlorine?

Bohr Model of an Ion Remember, an ion is an atom that has gained a charge (by either losing or gaining one or more electrons) The Bohr model indicates the charge with a “+ or –” and brackets. Note

Bohr model of ions Sodium atom Sodium ion Sodium ion has lost it’s outer most electron (-) to become more stable (like the noble gases) and now has a positive charge, indicated by the + and brackets.

Practice: Draw the Bohr model diagram for an aluminium atom and ion. aluminum-27 atom: aluminium-27 ion:

Draw the Bohr model diagram for an aluminium atom and ion. aluminum-27 atom: aluminium-27 ion:

Periodic Table and Ion Formation: Elements on the Left of the Periodic Table (metals) lose electrons and become positive ions (called cations) Elements on the Right (Non-metals) tend to gain electrons and become negative ions (called anions)

Forming Compounds: When two atoms get close together, their valence electrons interact. If the valence electrons can combine to form a low-energy bond (to become more stable), a compound is formed. Each atom in the compound attempts to have the stable number of valence electrons as the nearest noble gas.

Ionic Bonds: Ionic bonds form when electrons are transferred from cations (+) to anions (-). involves a metal (+) and a non-metal (-) For example, lithium and oxygen form an ionic bond in the compound Li2O

Bohr Model of an Ion The Bohr model indicates the charge with a “+ or –” and brackets. Note

Bohr Model of Ionic bond Bohr diagram of CaF2 Notice that each balance shell is full, making the element resemble the nearest noble gas

Bohr Model of Ionic Bond

Ionic Compounds Ionic substances form structured lattices containing oppositely charged ions. They have high melting and boiling points, conduct electricity when melted or dissolved in water. Eg NaCl. LiCa

Covalent Bonds: form when electrons are shared between two non-metals. Electrons stay with their atom, but overlap with other shells

Covalent Bonds A covalent bond, also called a molecular bond A molecule is an electrically neutral group of two or more atoms held together by chemical bonds.  Molecules are distinguished from ions by their lack of electrical charge. The pair of electrons involved in the bond is called a bonding pair.

Covalent compounds Involve non-metals only. Have lower melting points than ionic compounds (due to weaker bonds) Do not conduct electricity when solid or dissolved (no ions)

Bohr Diagram of Covalent bonds Because a covalent bond means electrons are shared, valence electrons overlap (spending time orbiting both elements) indicated by shell from each element in the bond touching.

Bohr Diagram of Covalent bonds

Check your understanding What types of elements form ionic bonds? What is the main difference between ionic and covalent bonds? Metal and non-metal Electrons are lost/gained or shared.

Lewis Diagrams: Invented by an American chemist Gilbert Lewis (1875 – 1946) Demonstrates chemical bonds by only showing the valence electrons and symbol. Example: Nitrogen atom

Lewis Diagrams: Note: the Lewis diagrams are the same (except for the symbols) for elements in the same family because they have the same number of valence electrons

Rules for drawing Lewis Diagrams Dots representing valence electrons are placed around the element symbol (on 4 sides, imagine a box around the symbol) Dots are placed singly, until the fifth electron is reached, then they are paired.

Lewis Diagrams for Ions: For positive ions: one electron dot is removed from the valence shell for each positive charge of the ion. Because only valence electrons are shown in Lewis diagrams, the positive ion usually not have any valence electrons left to show.

Lewis Diagrams for Ions: For negative ions: one electron dot is added to each valence shell for each negative charge of the ion. Usually means the symbol is surrounded by all 8 dots. Place Square brackets around each ion to indicate the proper charge.

Lewis Diagram for Ionic Compound

Lewis Diagrams For Covalent Bonds: The shared pairs of electrons are usually drawn as a straight line Like Bohr diagrams, valence electrons are drawn to show sharing of electrons. All atoms “like” to have a full valence shell

Bonding pairs, lone pairs Valence electrons involved in the bonding are called a bonding pair. Valence electrons NOT involved in the bond are called lone pairs.

Lewis Diagram for Diatomic Molecules Diatomic molecules are molecules composed of only two atoms. This makes them more stable than individual atoms. of the same or different chemical elements. The prefix di- is of Greek origin, meaning "two". If a diatomic molecule consists of two atoms of the same element, such as hydrogen (H2) or oxygen (O2), then it is said to be homonuclear.diatomic molecule: Diatomic molecules are molecules composed of only two atoms,

Oxygen forms a diatomic molecule

How would you draw a Lewis diagram for diatomic molecule of Nitrogen?

How would you draw a Lewis diagram for diatomic molecule of Nitrogen?