The Periodic Table & Atomic Structure 2.1

CHAPTER 6 Matter is made of atoms and every element has its own unique type of atom. Elements are identified by names and chemical symbols. Atoms have a structure that determines their properties. Every atom is composed of three types of subatomic particles: protons, neutrons, and electrons. The number of electrons in the outer shell of an element’s atoms determines the properties of the element. Ch. 2

6 The Periodic Table organizes elements in different ways. CHAPTER 6 The Periodic Table organizes elements in different ways. Metals are found on the left, non-metals on the right, and metalloids in between. Chemical families are arranged in vertical groups. Periodic Tables can indicate the chemical symbol, atomic number, atomic mass, ion charge, density, and other information about each element. Ch. 2

Elements are listed in order by atomic number Rows of elements (across) are called periods. All elements in a family have similar properties, and bond with other elements in similar ways Group 1 = alkali metals Group 2 = alkaline earth metals Group 17 = the halogens Group 18 = noble gases Ch. 2

CHAPTER 6 Ch. 2

6.1 VOCABULARY physical properties chemical properties mixtures pure substances elements atoms compounds Physical properties can be observed without changing the chemical structure of a substance. Chemical properties describe a possible chemical change. Ch. 2

6.2 The Nucleus Ch. 2

Atomic Theory VOCABULARY Ch. 2 subatomic particles nucleus protons neutrons atomic number mass number atomic mass electrons electron shells unpaired electrons paired electrons Ch. 2

area surrounding the nucleus Atomic Theory Name Symbol Charge Location Relative Mass Proton p 1+ nucleus 1836 Neutron n Electron e 1– area surrounding the nucleus 1 Ch. 2

6.2 Every atom of any one element will have the same number of protons Atomic number = # of protons = # of electrons There are an equal number of protons and electrons in an atom. Ions form when the number of electrons changes. The number of electrons in the outer shell determines the properties of the element. Ch. 2

Bohr Diagrams Bohr diagrams show how many electrons appear in each electron shell around an atom. Each shell holds a maximum number of electrons 2 electrons in the first shell, 8 in the 2nd shell, and 8 in the 3rd shell. Electrons in the outermost shell are called valence electrons Think of the shells as being 3D like spheres, not 2D like circles Ch. 2

The period # = # of shells in the atom. Except for the transition elements, the last digit of the group # = # of electrons in the valence shell Ch. 2

Bohr Diagrams What element is this? Ch. 2

Bohr Diagrams 18 p 22 n Argon! 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 Ch. 2

Patterns of Electron Arrangement in Periods and Groups The noble gas elements have full electron shells, and are very stable. Ch. 2

The Periodic Table Ch. 2 Where are the following? Atomic Number Period 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 Ch. 2