Joy of Science Discovering the matters and the laws of the universe

Joy of Science Discovering the matters and the laws of the universe Key Words Universe, Energy, Quantum mechanics, Chemical reaction, Structure of matter Unless otherwise noted, all copied pictures are taken from wikipedia.org

Review1 n The double-slit experiment was important in documenting 1. the small uncertainty of large object 2. the large uncertainty of small object 3. the wave-particle duality 4. the Heisenberg principle

Review 2 n The principle of uncertainty was originally proposed by 1. Dalton 2. Heisenberg 3. Thomson 4. Bohr

Review 3 n A quantum leap occurs when a(n).. moves between energy levels in an atom 1. proton 2. neutron 3. electron 4. photon

Review 4 n Because of the uncertainty principle, scientists are forced to rely on to describe the position of a small object whose velocity is known 1. probability 2. Newton s law s of motion 3. the wave-particle duality 4. hypothetical estimates

December 19, 2016 Atoms in combinations: the chemical bonds What happens to all thrown-away stuff after it becomes trash? Today s Keywords Chemical bond - ionic bond, metallic bond, covalent bond, hydrogen bond

Contents n Introduction n Electron shells and chemical bonds n Type of chemical bonds

Introduction n Most substances we find around us are composed of multi-elements Ex) Oxygen gas: O 2 (O + O) Water: H 2 O (2H + O) Salt: NaCl (Na + Cl)

Introduction n Most substances we find around us are composed of multi-elements Ex) Oxygen gas: O 2 (O + O) Water: H 2 O (2H + O) Salt: NaCl (Na + Cl) n Let s think about how elements can interact and link together Chemical bonding: the process by which two or more atoms combine Chemical bond: the linkage between two atoms

Hint of chemical bonding n Hint of chemical bonding is, O H H H 2 O

Hint of chemical bonding n Hint of chemical bonding is, the structure of atom: only light electrons in an atom can interact when another atom approaches to the atom but not heavy core, the nucleus O H H

1. Electron shells and chemical bonds - Valence electrons - The periodic table of elements - Electron shells and chemical bonds

Valence electrons n Think about how two atoms might interact - Atom: tiny dense nucleus (positive charge) at center + Electrons (negative charge) in orbital shells

Valence electrons n Think about how two atoms might interact - Atom: tiny dense nucleus (positive charge) at center + Electrons (negative charge) in orbital shells è mostly empty space

Valence electrons n Think about how two atoms might interact - Atom: tiny dense nucleus (positive charge) at center + Electrons (negative charge) in orbital shells è mostly empty space - When two atoms approach each other, their outer electrons encounter first.

Valence electrons n Think about how two atoms might interact (cont d) - Chemical bonding involves an exchange or sharing of valence electrons - The number of electrons in an atom s outermost shell is called valence Valence of Oxygen: 6 Hydrogen: 1

The Periodic table of the elements n All known chemical elements systemized in a table

The Periodic table of the elements n All known chemical elements systemized in a table provides a powerful framework for understanding the structure and interactions of atoms è The Periodic table of the elements

The Periodic table of the elements (cont d) * Weight of elements: Left à Right increase * Each vertical column: similar chemical properties

The Periodic table of the elements (cont d) The top three rows of the periodic table of the elements provide the key to understanding the varied strategies of chemical bonding. Top three rows

The Periodic table of the elements (cont d) The most stable arrangement of electrons has completely filled electron shells atomic number 2,10,18, and 36. The atoms do not react with other elements.

The Periodic table of the elements (cont d) The most stable arrangement of electrons has completely filled electron shells atomic number 2,10,18, and 36. The atoms do not react with other elements. è Atoms that do not have the magic number of electrons are more likely to react with other atoms to produce a stable energy state.

Concentric arrangement of electron shells 1 n The pattern of the elements in the periodic table mirrors a concentric arrangement of electrons into shells Period 1: One shell Period 4: four shells

Concentric arrangement of electron shells 2 n The pattern of the elements in the periodic table mirrors a concentric arrangement of electrons into shells Period 1: One shell Period 4: four shells Let s compare atomic number 17 element Cl & number 18 element Ar

Concentric arrangement of electron shells 3 17 Cl in period 3 1 st shell: two electrons 2 nd shell: eight electrons 3 rd shell: seven electrons 18Ar in period 3 1 st shell: two electrons 2 nd shell: eight electrons 3 rd shell: eight electrons Each shell has own capacity for electrons (K, L, M, N, O, P, G) 1 st shell s capacity: 2 2 nd shell s capacity:2+6=8 3 rd shell:2+6+10=18 4 th shell: 2+6+10+14=32 Each shell has subshells. (s, p, s, f, g) 1 st subshell: two electrons 2 nd subshell: six electrons 3 rd subshell: 10 4 th subshell: 14

Concentric arrangement of electron shells 4 17 Cl in period 3 1 st shell: two electrons 2 nd shell: eight electrons 3 rd shell: seven electrons 18Ar in period 3 1 st shell: two electrons 2 nd shell: eight electrons 3 rd shell: eight electrons 3 rd shell has completely filled subshellsà Stable! Each shell has own capacity for electrons. 1 st shell s capacity: 2 2 nd shell s capacity:2+6=8 3 rd shell:2+6+10=18 4 th shell: 2+6+10+14=32 Each shell has subshells. 1 st subshell: two electrons 2 nd subshell: six electrons 3 rd subshell: 10 4 th subshell: 14

Concentric arrangement of electron shells 5 One electron is less than Ar Stable! One electron is more than Ar Cl and K have tendency to take out or give off one electron

Reference n Pauli exclusion principle: No two electrons can occupy the same energy state at the same time. Each shell has a certain number of energy states and electrons fill the states according to Pauli s exclusion principle. electron spins (up- or down-spin state) also must be considered. Each shell is filled with a kind of spin state first and then the other type of spin fill the shell fully, and then once the shell is full the rest electrons move to the next shell with higher energy.

Any redistribution of electrons leading to more stable configuration between two or more atoms è Chemical bonds!

2. Types of chemical bonds - Three principal kinds of chemical bonds : ionic, metallic, and covalent - In addition, polarization and hydrogen bonding

Chemical bonding n Each type of bonding - corresponds to a different way of rearranging electrons

Chemical bonding n Each type of bonding - corresponds to a different way of rearranging electrons - produces distinctive properties in the materials it forms

Types of chemical bonds n Types of chemical bonds * Three principal types: ionic, metallic, covalent * Additional polarization and hydrogen bonding

Types of chemical bonds n Types of chemical bonds * Three principal types: ionic, metallic, covalent involve redistributing electrons between atoms * Additional polarization and hydrogen bonding result from shifts of electrons within their atoms or groups of atoms

Ionic bonds +, - n Two oppositely charged ions link together by electrical force è Ionic bonds

Ionic bonds +, - n Two oppositely charged ions link together by electrical force è Ionic bonds n Atoms with magic numbers of 2, 10, 18 electrons are particularly stable * Atoms that differ from these magic numbers by one electron in the outer orbit are particularly reactive è tend to fill or empty their outer orbits by taking out or giving off an electron

n magic numbers of 2, 10, 18: stable è rarely react * 3 Li, 11 Na, or 17 Cl are particularly reactive * Reactive atoms tend to fill or empty their outer orbits by taking out or giving off an electron

Ionic bonds (example reaction: Na + Cl) n For example, When you place sodium ( 11 Na: soft, silvery white metal) in contact with chlorine gas ( 17 Cl, yellow-green toxic gas), in fiery reaction, è Sodium Chloride (NaCl) www.ltcconline.net/stevenson

Ionic bonds (Na + Cl à NaCl: how?) n How? Neutral sodium has 11 positive protons in its nucleus, balanced by 11 negative electrons in orbit, so tend to loose an electron in order to make a magic number with 10 electrons. Neutral chlorine has 17 positive protons and 17 negative electrons, so tends to make a magic number with 18 electron by obtaining an extra electron.

Ionic bonds (NaCl: Na + Cl -! ) n Resulting sodium and chlorine compounds are now ions in the form of Na + and Cl -, and the two oppositely charged ions link together by the electrical force è Ionic bonds!

Metallic bonds n * In a metal, atoms release their outer electrons to achieve the more stable configuration. Then, the extra electrons move away from their parent atoms to float around the metal, forming a kind of sea of negative charge. In a metal

Metallic bonds n * Atoms in a metal give up electrons, and the electrons are redistributed to be shared by many atoms è Metallic bond

Metallic bonds (cont d) n Metals are formed by any element or combination of elements in which large numbers of atoms share electrons to achieve a more stable arrangement * Some metals, such as aluminum, iron, copper and gold, are familiar * The great majority of chemical elements are known to occur in the metallic state * Two or more elements can combine to form a metal 合金 alloy, such as brass(copper + zinc) or bronze(copper + tin) * Modern specialty-steel alloys contain many different 特殊鋼合金 elements in careful control

Metallic bonds (cont d) n The nature of the metallic bond explains the distinctive properties of metals * It is hard to break the metallic bond just by pushing or twisting, because the atoms are able to rearrange themselves * * Electrical properties of materials with metallic bonds will be discussed in the next chapter

Covalent bonds n The covariant bond, the bonding type in between the ionic bond and the metallic bond, is in which welldefined clusters of neighboring atoms, called molecules. * The simplest covalently bonded molecules contain two atoms of the same element, such as the diatomic gases hydrogen (H 2 ), nitrogen (N 2 ), and oxygen (O 2 ).

Covalent bonds (example: H + H à H 2 ) n * For example,

Covalent bonds (H + H à H 2 : how?) n * For example, each atom in hydrogen has a relatively unstable single electron, so two hydrogen atoms pool their electrons to create a more stable two-electron arrangement when they approach closely to each other. Recall: 2He with two electrons is a stable atom

Covalent bonds carbon based n The most fascinating of all covalently bonded elements is carbon * In principle, carbon can create a compound with strong ionic bond between C 4+ and C 4-, and become a metal in which every carbon atom releases four electrons into an extremely dense electron sea è But, neither happens!

Covalent bonds carbon based (cont d) n The most fascinating of all covalently bonded elements is carbon (cont d) * The most is for the carbon atoms to share their outer electrons è Covalent bonds!!

Covalent bonds carbon based (cont d) n The most fascinating of all covalently bonded elements is carbon (cont d) * The most is for the carbon atoms to share their outer electrons è Covalent bonds!! Once bonds between carbon atoms have formed, the atoms have to stay close to each other for the sharing to continue, just like the bond in the case of hydrogen

Covalent bonds carbon based * By forming bonds among several adjacent carbon atoms, you can make rings, long chains, branching structures, planes, and three-dimensional frameworks of carbon

Covalent bonds carbon based (cont d) n The most fascinating of all covalently bonded elements is carbon (cont d) * The study of carbon-based molecules is called organic chemistry. *Molecules in every living thing are held together in part by covalent bonds in carbon. * Covalent bonds play an important role to carry the genetic code in DNA. è The covalent bond is the bond of life * Covalent bonds play a crucial role in the silicon-based circuits, such as in computers.

Hydrogen bonds n A weak bond that forms after a hydrogen atom links to an atom of certain other elements (oxygen or nitrogen, for example) by a covalent bond is the hydrogen bond (1 in the picture shown below). 105 o The bond between water molecules

Hydrogen bonds * Each water molecule (H 2 O) is formed from two hydrogen atoms and one oxygen atom, arranged at 105-degree angle. 105 o

http-//alevelnotes.com Polarization * Rearrangement of electrical charge: Hydrogen part of the water molecule has more positive charge and the oxygen part has more negative charge than another even though the molecule itself is electrically neutral A molecule: neutral More - More +

http-//alevelnotes.com Polarization * Rearrangement of electrical charge: (cont d) è Attract between the negative end of the molecule and the positive side of the other molecule è Polarization! + + +

Polarization and hydrogen bonds n Molecules also experience forces that hold one to another by the electrical forces from polarization generated in hydrogen bonds n Individual hydrogen bonds are weak, but in many molecules they occur repeatedly and therefore play a major role in determining the molecule s shape and function. (It is responsible for the high boiling point of water, and responsible for structures of proteins and nucleic acids the building block of DNA- and the structure of polymers.) n Hydrogen bonds are common in all biological substance. They form the complex structures of every cell in our body.

Polarization and hydrogen bonds DNA double helix structure Examples cytosine Guanine Bonding between two base pairs in DNA Hydrogen bonds Acetic acid

Modern materials: chapter 7 on January 16, 2017 Merry Christmas! and Happy New Year!!!