Physical Science Chpt. 10 Atomic Structure The Periodic Table Isotopes

Chemical Symbols Abbreviations of an element –C = carbon –H = Hydrogen –Ca = calcium –One capital letter or one capital letter and one small letter

Atoms Parts –Protons—positive charge –Neutrons—neutral charge –Electrons—negative charge Mass of proton and neutron is equal—relative mass of 1 Mass of electrons is 1/2000 mass of a proton— relative mass of 0 Democritus –Stated that matter is made of particles that we call atoms Atom is the smallest particle into which an element can be divided and still be the same substance

Atoms Basic building blocks of matter Atoms must have equal numbers of protons and electrons to be neutral –More electrons—negatively charged atom –More protons—positively charged atom Electron cloud surrounds the nucleus and contains electrons Penny has 2 X nd power atoms

Forces in Atoms Gravitational Force—acts between all objects at all time, amount of gravitational force depends on masses and distance between objects Electromagnetic Force—opposite charges attract and same charges repel, protons and electrons attract, holds electrons around the nucleus Strong Force—keeps protons from flying apart, at close distances the strong force is greater than electromagnetic force and therefore the nucleus stays together Weak Force—impt. In radioactive atoms, in unstable atoms, a neutron can change into a proton and an electron

Atomic Number The number of protons in the nucleus Number of protons and electrons when the atom is NEUTRAL

Atom Scientists Scientists- –Used probability model to guess where electrons could be located Rutherford –Designed an experiment to study the parts of an atom –He aimed a beam of small, positively charged particles at a thin sheet of gold foil –Found that some particles were deflected, some came straight back and some went right through Bohr –Early model of an atom central nucleus with electrons around –Electrons move in paths and can jump levels Dalton –Atomic theory All substances are made of atoms. Atoms are small particles that cannot be created, divided or destroyed Atoms of the same elements are exactly alike, and atoms of different elements are different Atoms join with other atoms to make new substances Not exactly correct Thomson –Proposed that electrons were located throughout an atom like plums in a pudding

Modern Atomic Theory Erwin Schrodinger and Werner Heisenberg Explained the nature of electrons, do not travel in definite paths Regions where electrons are likely to be found Electron Cloud Model

Electron Levels 1 st level—2 electrons 2 nd level—8 electrons 3 rd level—18 electrons 4 th level—32 electrons Electrons closest to the nucleus have low energy Electrons farther away from nucleus have more energy

Atomic Mass Unit Proton and neutron equal Defined as one twelfth the mass of carbon

Mass Number Is the sum of the number of protons and the number of neutrons in the nucleus

Isotopes Atoms of the same element that have different numbers of neutrons Example –Boron-10—5 protons and 5 neutrons –Boron-11—5 protons and 6 neutrons –Hydrogen has 3 isotopes, 0 neutrons, 1 neutron and 2 neutrons, always one proton otherwise it wouldn’t be hydrogen –The number of protons determines the element

Average Atomic Mass Is given to all elements because they each have more than one isotope Defined –Average mass of the mixture of isotopes –The average atomic mass is always closest to the mass of its most abundant isotope

Periodic Table Dimitri Mendeleev –Was first to develop a periodic table –He could predict missing element’s properties –Used the game concentration to figure out the periodic table

Periodic Table Moseley –Arranged the periodic table based on atomic number and not atomic mass

Periodic Table In your textbook found on pages

Periodic Table Groups of elements (families) Vertical columns—groups or families #1-18 Elements in groups have similar properties Dot diagram uses the symbol of the element and dots to represent the electrons in the outer level page 289

Periodic Table Families/groups –All have the same number of electrons in the outer energy level

Periodic Table Periods of elements –Horizontal rows

Periodic Table Dark line separates metals from nonmetals and metalloids touch the line Metals –Normally solids at room temperature, shiny, good conductors of heat and electricity Nonmetals –Normally gases or brittle solids, not good conductors Metalloids –Properties of both metals and nonmetals

Periodic Table Transition Elements –Groups 3-12 –Properties vary –Outer energy level electrons vary