Chapter 6 The Periodic Table & Periodic Law Mr. Stripling Pre-AP Chemistry Room 402

Development of the Periodic Table Early model by Antoine Lavoisier

John Newlands Proposed an organizational scheme for elements When elements are arranged by atomic mass, properties repeated every eighth element Repeating pattern = PERIODIC

Problems with the law of octaves: But… Newlands called it the law of octaves (after the musical octave where notes repeat every eighth tone) Problems with the law of octaves: Did not work with all known elements Fellow scientists hated octave (too unscientific for them) Over the years Newlands was found to be basically correct. There WAS a repeating (PERIODIC) pattern for the properties of elements

Dmitri Mendeleev, 1869 Demonstrated connection between atomic mass and elemental properties Organized elements by increasing atomic mass into columns with similar properties Predicted properties of undiscovered elements that have since been found

Mendeleev’s version was not 100% correct The arrangement of elements by mass resulted in elements of different properties being placed together Mosely, 1913 Discovered elements contain a unique number of protons Mosely arranged elements by increasing atomic number Resulted in a clear periodic pattern of properties Came to be known as periodic law

The Modern Periodic Table Consists of boxes containing the element name, symbol, atomic number, and atomic mass These boxes are arranged in order of increasing atomic number into a series of columns called groups/families and rows called periods

Total number of periods = 7 Total number of groups/families = 18 Elements in groups 1, 2, and 13-18 are referred to as representative elements due to possessing a wide range of chemical and physical properties Elements in groups 3-12 are classified as transition elements

Metals are element that are generally shiny when smooth and clean, solid at room temperature, and good conductors of heat and electricity Most metals are malleable and ductile

Group 1 elements (EXCEPT HYDROGEN) are known as the alkali metals Due to having a high reactivity, alkali metals typically are found as compounds (chemical combination of two or more elements)

Group 2 is made of the alkaline earth metals which also possess a level of high reactivity

The transition elements are divided into transition metals and inner transition metals The two sets of inner transition metals are known as the lanthanide and actinide series are located at the bottom of the periodic table The rest of the elements in groups 3-12 make up the transition metals

Nonmetals are elements that are usually gases or brittle, dull-looking solids Nonmetals are poor conductors of heat and electricity

Halogens comprise group 17 of the periodic table Halogens are highly reactive and are also often found as parts of compounds

Noble gases comprise group 18 Noble gases are extremely unreactive Used in lasers, light bulbs, and neon signs

Metalloids have physical and chemical properties of both metals and nonmetals

Classwork Problems 4, 5, and 7 on page 181 Due tomorrow

Classification of the Elements Valence electrons are the electrons in the highest principal energy level of an atom Group 1 elements have similar chemical properties because they have the same number of valence electrons

The s-, p-, d-, and f-Block Elements Because there are four different energy sublevels (s, p, d, and f) the periodic table is divided into four blocks, giving the table it’s odd shape

The s-block is made of groups 1 and 2, plus helium Group 1 elements have partially filled s orbitals containing one valence electron and an electron configuration ending in s1 Group 2 elements have completely filled s orbitals containing two valence electrons and an electron configuration ending in s2

After the s sublevel is filled the valence electrons next fill the p sublevel The p-block is comprised of groups 13-18 The three p orbitals can hold a maximum of six electrons

The d-block contains the transition metals The aufbau principle states that the 4s orbital has a lower energy level than the 3d orbitals and is therefore filled first The five d orbitals can hold ten electrons That is why the d-block spans ten groups on the periodic table

The f-block contains the inner transition metals Characterized by a filled or partially filled s orbitals and filled or partially filled 4f and 5f orbitals The electrons of the f sublevel are not always predictable Has seven orbitals and spans 14 columns on the periodic table

Classwork Do problems 8, 9, 10, and 12 on page 186 Due Monday

Periodic Trends – Atomic Radius Atom size is dependent on electron configuration Atom size is defined by how close an atom is to another atom Atomic Radius – half the distance between adjacent nuclei in a crystal of an element Elements that occur as molecules, atomic radius is defined as half the distance between nuclei of identical atoms that are chemically bonded together

There is a decrease in atomic radii going from left to right across a period Decreasing atomic radii is caused by increasing positive charge

Atomic radii increases as you move down a group The increased number of orbitals means that electrons are further from the nucleus, increasing the atomic radius

Ionic Radius Ions are formed by atoms gaining or losing electrons Ion – an atom or a bonded group of atoms that has a positive or negative charge Atoms that lose electrons and form positively charged ions become smaller The electron lost will be a valence electron, resulting in a smaller radius

Atoms that gain electrons gain a negative charge and become larger

In general, moving left to right across a period, the size of positive ions decrease In groups 15 and 16, the size of the negative ions also begin to decrease Moving down groups, the size of the ionic radii tend to increase

Ionization Energy The energy required to remove an electron from a gaseous atom How strongly an atom’s nucleus holds onto its valence electrons High ionization energies indicate atoms are less likely to lose electrons

When a sodium atom loses its single valence electron to form a 1+ sodium ion, its electron configuration changes The new configuration matches neon, demonstrating the octet rule Octet rule – atoms tend to gain, lose, or share electrons in order to acquire a full set of 8 valence electrons

Electronegativity Indicates the relative ability of an element’s atoms to attract electrons in a chemical bond Tends to decrease while moving down groups Tends to increase moving left to right across a period

Classwork – Section 6.3 #16 & 19 on page 189 #21 on page 194 Due tomorrow