Chem 1103 Lecture 1 PDF

CHEM 1103 Chemistry for Engineers Marcelino Dela Rama Tradio Jr., RCh, LPT, PhD-Chem Chemistry Analytical and Environmental Section (ChAnELS) Departmen...

CHEM 1103 Chemistry for Engineers Marcelino Dela Rama Tradio Jr., RCh, LPT, PhD-Chem Chemistry Analytical and Environmental Section (ChAnELS) Department of Chemistry School of Arts and Sciences University of San Carlos Nasipit Talamban Cebu City 6000, Philippines The capacity to learn is a gift. The ability to learn is a skill. The willingness to learn is a choice.” – Brian Herbert “ Atomic Structure and Engineering Materials Levels of Structure of Materials 1. atomic structure (∼10-10 m or 1 angstrom) 2. short – range and long – range atomic arrangement 3. nanostructure (length scale: 1 to 100 nm) 4. microstructure (length scale: 100 to 100 000 nm to 100 𝜇m) 5. Macrostructure (length scale: > 100 𝜇m) - The features of the structure of each of these levels may have distinct and profound influences on a materials’ properties and behavior. Atomic Structure and Engineering Materials Levels of Structure of Materials 1. atomic structure (∼10-10 m or 1 angstrom) Atomic Structure and Engineering Materials Levels of Structure of Materials 2. short – range and long – range atomic arrangement Atomic Structure and Engineering Materials Levels of Structure of Materials 3. nanostructure (length scale: 1 to 100 nm) Atomic Structure and Engineering Materials Levels of Structure of Materials 4. microstructure (length scale: 100 to 100 000 nm to 100 𝜇m) Atomic Structure and Engineering Materials Levels of Structure of Materials 5. Macrostructure (length scale: > 100 𝜇m) Atomic Structure and Engineering Materials Why we need to examine the structure of atoms in studying engineering materials? o structure of the atom determine the nature of atomic bonding – dictates the physical and mechanical properties of the materials o affects the suitability of materials for real-world engineering applications. o Strong bonds that constitute the materials would have high melting temperature, high modulus of elasticity, and low coefficient of thermal expansion o We need to understand the bonding in the material and make efforts to tailor it so that certain performance requirements are met. Structure of an Atom o Atom is composed of nucleus surrounded by electrons. o The nucleus contains neutron and positively-charged protons o The negatively-charged electrons are held to the nucleus by electrostatic attraction o The electric charge, q, carried by each electron and proton is 1.60 x 10-19 Coulomb o Atomic number of an element is equal to the number of protons in each atom. o Number of proton is equal to number of electron for neutral atom Structure of an Atom Example 1: 1. Determine the number of protons, neutrons, and electrons of F-20. 2. How many protons, electrons, and neutrons are found in a Cl- ion formed from Cl-35? 3. Which of the two ions below have the same number of electrons? Structure of an Atom o The mass of each proton and neutron is 1.67 x 10-24 g, but the mass of each electron is only 9.11 x 10-28 g o Atomic Mass M is equal to the total mass of average number of protons and neutrons in an atom in atomic mass units, which is also the mass in grams of the Avogadro’s constant NA of atoms. o NA = 6.022 x 1023 atoms or molecules/mole o the unit of atomic mass is g/mol or amu (1/12 the mass of carbon 12) Structure of an Atom Example 2: Calculating the number of atoms in silver Calculate the number of atoms in 100 g of silver (Ag). Structure of an Atom Example 3: Calculating the number of atoms in iron nanoparticles Calculate the number of atoms of iron nanoparticle that has 3 nm diameter. Consider that the shape of iron nanoparticle is spherical and it has a density of 7.8 g/cm3. The atomic mass of iron is 55.847 g/mol. Electronic Structure of an Atom § electrons occupy discrete energy levels within the atom. § each electron possesses a particular energy with no more than two electrons in each atom having the same energy. § each element possesses different set of these energy levels § The energy level to which each electron belongs is defined by four quantum numbers. § Principal quantum number (n)– reflects the grouping of electrons into sets of energy levels (quantum shell) § Azimuthal quantum number (l) – energy levels within each shell and reflect grouping of similar energy levels (orbitals); n-1 § Magnetic quantum number (ml) – specifies the orbitals associated with a particular azimuthal quantum number within each shell; 2l +1 § Spin quantum number (ms) – reflects the two possible values of “spin” of each electron (assigned values of +1/2 and -1/2) Electronic Structure of an Atom Pauli’s Exclusion Principle – no two electron can have the same set of quantum numbers; each orbital has two electrons, one “spin up”, the other, “spin down” in each orbital Electronic Structure of an Atom Electronic Structure of an Atom Electronic Structure of an Atom § Electron Configuration – shorthand notation to denote electronic structure of an atom (with numerical value of principal quantum number, the lowercase letter notation for the azimuthal quantum number, and a superscript showing the number of electrons in each type of orbital. § Reflect the distribution of electrons among the orbitals. § The electrons are filled in according to a scheme as Aufbau Principle “building up”, which corresponds to increasing energy of the subshells. Electronic Structure of an Atom Hund’s Rule – states that orbitals of equal energy are each occupy by one electron before any orbital is occupied by a second electron and that each of the single electrons must have the same spin. Electronic Structure of an Atom Electronic Structure of an Atom Electronic Structure of an Atom Valence of an atom § Number of electrons in an atom found in the outermost shell (e.g. s and p shells) that participate in bonding or chemical reactions. Mg : 1s2 2s2 2p6 3s2 valence = 2 Al : 1s2 2s2 2p6 3s23p1 valence = 3 Si : 1s2 2s2 2p6 3s23p2 valence = 4 END