Atoms, Ions and Molecules College of Biotechnology General Chemistry Lecture 2 Dr. M. Abd-Elhakeem
Composition of Matter • Matter - Everything in universe is composed of matter • Matter is anything that occupies space or has mass • Mass – quantity of matter an object has • Weight – pull of gravity on an object
Elements • Pure substances that cannot be broken down chemically into simpler kinds of matter • More than 100 elements
Compounds Most elements do not exist by themselves Readily combine with other elements in a predictable fashion
A compound is a pure substance made up of atoms of two or more elements The proportion of atoms are always fixed
Atoms • The simplest particle of an element that retains all the properties of that element • Properties of atoms determine the structure and properties of the matter they compose • Our understanding of the structure of atoms based on scientific models, not observation
The Nucleus • Central core • Consists of positive charged protons and neutral neutrons • Positively charged • Contains most of the mass of the atom
The Protons • All atoms of an element have the same number of protons • Number of protonsbalanced by an equal number of negatively charged electrons
The Neutrons • The number varies slightly among atoms of the same element • Neutrons are neutral charged
The Electrons • Negatively charged high energy particles with little or no mass • Travel at very high speeds at various distances (energy levels) from the nucleus
Dalton’s Atomic Theory (1808) • All matter is made of tiny indivisible particles called atoms. • Atoms of the same element are identical. The atoms of any one element are different from those of any other element.
3. Atoms of different elements can combine with one another in simple whole number ratios to form compounds. 4. Chemical reactions occur when atoms are separated, joined, or rearranged; however, atoms of one element are not changed into atoms of another by a chemical reaction.
J.J. Thomson’s cathode ray tube: discovery of electrons and the e- charge-to-mass ratio • In a vacuum chamber, flow of high voltage (emitted from cathode to anode) is deflected by magnetic & electrical fields
Thomson’s Atomic Model Thomson believed that the electrons were like plums embedded in a positively charged “pudding,” thus it was called the “x” model.
Ernest Rutherford’sGold Foil Experiment - 1911 • Alpha particles are helium nuclei - The alpha particles were fired at a thin sheet of gold foil • Particles that hit on the detecting screen (film) are recorded
Most of the particles passed right through • A few particles were deflected • VERY FEW were greatly deflected Conclusions: The nucleus is small The nucleus is dense The nucleus is positively charged
The atom is mostly empty space • All the positive charge, and almost all the mass is concentrated in a small area in the center. He called this a “nucleus” • The nucleus is composed of protons and neutrons (they make the nucleus!) • The electrons distributed around the nucleus, and occupy most of the volume
Niels Bohr 1913 studied under Rutherford at the Victoria University in Manchester. Bohr refined Rutherford's idea by adding that the electrons were in orbits. Rather like planets orbiting the sun. With each orbit only able to contain a set number of electrons.
Bohr Model • According to Bohr’s atomic model, electrons move in definite orbits around the nucleus, much like planets circle the sun. • These orbits, or energy levels, are located at certain distances from the nucleus.
Energy Levels Atoms have 7 energy levels The levels are K (closest to the nucleus), L, M, N, O, P, Q (furthest from the nucleus) The K level can only hold 2 electrons Levels L can hold 8 electrons
Electrons in the same energy level are approximately the same distance from the nucleus Outer energy levels have more energy than inner levels
Sub shell (atomic orbital) • Each shell is composed of one or more subshells, which are themselves composed of atomic orbitals. For example, the first (K) shell has one subshell, called "1s"; the second (L) shell has two subshells, called "2s" and "2p"; the third shell has "3s", "3p", and "3d"; and so on
s orbital has spherical form • p orbital is composed of three degenerate dumbbell-shaped orbitals px, py, pz • d orbital is composed of five degenerate orbitals • fis composed of seven degenerate orbitals • Each orbital is occupied with 2 electrons
Maximum number of electrons in each subshell: s=2, p=6, d=10, f=14 • Order for filling subshells: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p where the number indicates the energy level and the letter indicates the subshell being filled
Atomic Number • This refers to how many protons an atom of that element has. • No two elements, have the same number of protons.
Atomic Mass • Atomic Mass refers to the “weight” of the atom. • It is derived at by adding the number of protons with the number of neutrons. This is a helium atom. Its atomic mass is 4 (protons plus neutrons). What is its atomic number? H
While most atoms have the same number of protons and neutrons, some don’t. • Some atoms have more or less neutrons than protons. These are called isotopes. • An atomic mass number with a decimal is the total of the number of protons plus the average number of neutrons.
Ion • An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive (cation) or negative (anion) electrical charge.
In this chapter What is atom, ion, molecule, and isotope. Atomic composition. Electron configuration. Atomic number, atomic weight. Story of the atom.