Cross-Disciplinary: Seeing Atoms - The STM

Cross-Disciplinary: Seeing Atoms - The STM Image of reconstruction on a clean gold surface. STM image of graphite Silicon diode

Section 1 Atomic Structure Chapter 4 Objectives • ExplainDalton’s atomic theory, and describe why it was more successful than Democritus’s theory. • State the charge, mass, and location, of each part of an atom according to the modern model of the atom. • Compare and contrast Bohr’s model with the modern model of the atom.

Section 1 Atomic Structure Chapter 4 What Are Atoms? • Our understanding of atoms required many centuries. • The idea of an atom—which means “unable to be divided”—dates back to the Greek philosopher Democritus, who lived in the fourth century BCE. • John Dalton developed an atomic theory in 1808. • Like Democritus, Dalton proposed that atoms could not be divided. Dalton’s was the first atomic theory with a scientific basis.

Section 1 Atomic Structure Chapter 4 What Are Atoms? continued • An atom is the smallest part of an element that still has the element’s properties. • Atoms are the building blocks of molecules.

Section 1 Atomic Structure Chapter 4 What’s in an Atom? • Atoms are made of protons, neutrons, and electrons. • At the center of each atom is a small, dense nucleus with a positive electric charge. • The nucleus is made of protons (a subatomic particle that has a positive charge) and neutrons (a subatomic particle that has no charge). • Moving around outside the nucleus is a cloud of electrons: subatomic particles with negative charges.

Section 1 Atomic Structure Chapter 4 What’s in an Atom? continued • Unreacted atoms have no overall charge. • Although atoms are made of charged particles, they do not have an overall charge because they have an equal number of protons and electrons whose charges exactly cancel. • To the right is shown a heliumatom, which is made of twoprotons, two neutrons, andtwo electrons.

Section 1 Atomic Structure Chapter 4 Models of the Atom • Bohr’s model compares electrons to planets. • In 1913, the Danish scientist Niels Bohr suggested that electrons in an atom move in set paths around the nucleus much like the planets orbit the sun in our solar system. • In Bohr’s model, electrons can only be in certain energy levels. Bohr’s model of electrons is illustrated on the following slide.

Section 1 Atomic Structure Chapter 4 Building Model

Section 1 Atomic Structure Chapter 4 Models of the Atom, continued • Electrons act more like waves. • By 1925, Bohr’s model of the atom no longer explained electron behavior. • A new model was proposed, in which electrons behave more like waves on a vibrating string than like particles.

Section 1 Atomic Structure Chapter 4 Models of the Atom, continued • An electron’s exact location cannot be determined. • It is impossible to determine both the exact location of an electron in an atom and the electron’s speed and direction. • The best scientists can do is calculate the chance of finding an electron in a certain place within an atom.

Section 1 Atomic Structure Chapter 4 Models of the Atom, continued • Electrons exist in energy levels. • The number of filled energy levels an atom has depends on the number of electrons. • The figure to the right shows how the first four energy levels are filled.

Section 1 Atomic Structure Chapter 4 Models of the Atom, continued • Electrons are found in orbitals within energy levels. • An orbital is a region in an atom where there is a high probability of finding electrons. • An s orbital is shaped like a sphere: • A p orbital is dumbbell shaped and can be oriented three different ways in space:

Section 1 Atomic Structure Chapter 4 Models of the Atom, continued • Every atom has between one and eight valence electrons. • Valence electrons are found in the outermost shell of an atom and determine the atom’s chemical properties. • Valence electrons are the electrons in an atom that participate in chemical bonding.

Section 1 Atomic Structure Chapter 4 Valence Electrons

Section 2 A Guided Tour of the Periodic Table Chapter 4 Objectives • Relatethe organization of the periodic table to the arrangement of electrons within an atom. • Explain why some atoms gain or lose electrons to form ions. • Determine how many protons, neutrons, and electrons an atom has, given its symbol, atomic number, and mass number. • Describe how the abundance of isotopes affects an element’s average atomic mass.

Section 2 A Guided Tour of the Periodic Table Chapter 4 Organization of the Periodic Table • The periodic table groups similar elements together. • This organization makes it easier to predict the properties of an element based on where it is in the periodic table. • Elements are listed in order of number of protons, because the periodic law states that when elements are arranged this way, similarities in their properties will occur in a regular pattern.

Section 2 A Guided Tour of the Periodic Table Chapter 4 Organization of the Periodic Table, continued • The periodic table helps determine electron arrangement. • Horizontal rows in the periodic table are called periods. • Just as the number of protons an atom has increases as you move from left to right across a period, so does its number of electrons.

Section 2 A Guided Tour of the Periodic Table Chapter 4 Organization of the Periodic Table, continued • Elements in the same group have similar properties. • A group is a vertical column of elements in the periodic table. • Atoms of elements in the same group have the same number of valence electrons, so these elements have similar properties.

Section 2 A Guided Tour of the Periodic Table Chapter 4 Some Atoms Form Ions • An ion is an atom or group of atoms that has lost or gained one electrons and has a negative or positive charge. • A lithium atom loses one electron to form a 1+ charged ion: • A fluorine atom gains one electron to form a 1 charged ion:

Section 2 A Guided Tour of the Periodic Table Chapter 4 Ion

Section 2 A Guided Tour of the Periodic Table Chapter 4 How Do the Structures of Atoms Differ? • The atomic number,Z, of an atom equals the number of protons in the nucleus. • The mass number,A, of an atom equals the number of protons plus the number of neutrons in the nucleus.

Section 2 A Guided Tour of the Periodic Table Chapter 4 Nucleus

Section 2 A Guided Tour of the Periodic Table Chapter 4 Atomic Number

Section 2 A Guided Tour of the Periodic Table Chapter 4 Mass Number

Section 2 A Guided Tour of the Periodic Table Chapter 4 How Do the Structures of Atoms Differ? continued • An isotope is an atom that has the same number of protons as other atoms of the same element do but that has a different number of neutrons. • Example: Hydrogen has three isotopes, shown below. • Some isotopes are more common than others.

Section 2 A Guided Tour of the Periodic Table Chapter 4 How Do the Structures of Atoms Differ? continued • If you know the atomic number and mass number of an atom, you can calculate the number of neutrons it has. • Example: uranium-235 has a mass number of 235. Like all uranium atoms, it has an atomic number of 92. The number of neutrons it has is therefore: Mass number (A): 235 Atomic number (Z): –92 Number of neutrons: 143

Section 2 A Guided Tour of the Periodic Table Chapter 4 Isotopes

Section 2 A Guided Tour of the Periodic Table Chapter 4 How Do the Structures of Atoms Differ? continued • Because the mass of a single atom is so tiny, atomic masses are usually expressed in atomic mass units. • An atomic mass unit (amu) is equal to one twelfth of the mass of a carbon-12 atom. • The average atomic mass for an element is a weighted average of the masses of all naturally-occurring isotopes of an element.

Section 2 A Guided Tour of the Periodic Table Chapter 4 Average Atomic Mass

Section 3 Families of Elements Chapter 4 Objectives • Locatealkali metals, alkaline-earth metals, and transition metals in the periodic table. • Locate semiconductors, halogens, and noble gases in the periodic table. • Relate an element’s chemical properties to the electron arrangement of its atoms.

Section 3 Families of Elements Chapter 4 How Are Elements Classified? • The elements are classified into three groups. • Most elements are metals, elements that are shiny and conduct heat and electricity well. • Nonmetals, all except hydrogen of which are found on the right side of the periodic table, may be solids, liquids, or gases at room temperature. • Between these groupings are semiconductors, elements that can conduct electricity under certain conditions.

Section 3 Families of Elements Chapter 4 How Are Elements Classified? continued • The periodic table below shows the distribution of metal, nonmetals, and semiconductors in the periodic table.

Section 3 Families of Elements Chapter 4 Metals • The alkali metals, found in Group 1 of the periodic table, are very reactive. • The alkaline-earth metals, whichinclude calcium, are found in Group 2 of the periodic table, andare somewhat less reactive than the alkali metals. • The transition metals, such as gold, iron, and mercury, occupy Groups3–12 of the periodic table.

Section 3 Families of Elements Chapter 4 Nonmetals • Carbon is found in three different forms and can form many compounds. • Nonmetals and their compoundsare plentiful on Earth. • Halogens, such as chlorine, arelocated in Group 17 of the periodic table. • Noble gases, such as neon, make up Group 18 of the periodic table. They are unreactive.

Section 3 Families of Elements Chapter 4 Nonmetals, continued • Semiconductors are intermediateconductors of heat and electricity. • Silicon is the most familiar semiconductor. • Silicon is an important part of computer chips, as well as other semiconductor devices such as transistors, LED display screens, and solar cells.

Section 4 Using Moles to Count Atoms Chapter 4 Objectives • Explainthe relationship between a mole of a substance and Avogadro’s constant. • Find the molar mass of an element by using the periodic table. • Solve problems converting the amount of an element in moles to its mass in grams, and vice versa.

Section 4 Using Moles to Count Atoms Chapter 4 Bellringer Sometimes when you are dealing with numbers of things, it is convenient to have a special unit that designates a specific number of the objects. Below are examples of special units that are used to count objects. 1. How many objects are in each sample?

Section 4 Using Moles to Count Atoms Chapter 4 Bellringer, continued 2. What if you want to use six sticks of butter, but you only have a large block of butter and a scale? How could you get the equivalent of six sticks of butter without the mess of dividing the large block into sticks?

Section 4 Using Moles toCount Atoms Chapter 4 Counting Things • There are many different counting units: for example, eggs are packaged by the dozen. • The mole is useful for counting small particles. • A mole (abbreviation: mol) is the number of particles that is the same as the number of atoms of carbon in 12 g of carbon-12. • Avogadro’s constant is the number of particles per mole of a substance: 6.022 × 1023

Section 4 Using Moles to Count Atoms Chapter 4 The Mole

Section 4 Using Moles to Count Atoms Chapter 4 Avogadro’s Number

Section 4 Using Moles toCount Atoms Chapter 4 Counting Things, continued • Moles and grams are related. • The mass in grams of 1 mol of a substance is called its molar mass. • For example, 1 mol of carbon-12 atoms has a molar mass of 12.00 g. • The molar mass of an element is its average atomic mass, which is listed in the periodic table.

Section 4 Using Moles to Count Atoms Chapter 4 Molar Mass

Section 4 Using Moles toCount Atoms Chapter 4 Calculating with Moles • To convert between moles and grams and vice versa, you can use a conversion factor: a ratio that is derived from the equality of two different units. • Let’s say that a shopkeeper knows that exactly 10 gumballs have a total mass of 21.4 g. This relationship can be written as either one of two equivalent conversion factors:

Section 4 Using Moles to Count Atoms Chapter 4 Conversion Factor

Section 4 Using Moles toCount Atoms Chapter 4 Math Skills Conversion Factors What is the mass of exactly 50 gumballs? 1. List the given and unknown values. Given:mass of 10 gumballs = 21.4 gUnknown: mass of 50 gumballs = ? g

Section 4 Using Moles to Count Atoms Chapter 4 Math Skills, continued 2. Write down the conversion factor that converts number of gumballs to mass. The conversion factor you choose should have the unit you are solving for (g) in the numerator and the unit you want to cancel (number of gumballs) in the denominator.

Section 4 Using Moles to Count Atoms Chapter 4 Math Skills, continued 3. Multiply the number of gumballs by this conversion factor, and solve. 107 g

Section 4 Using Moles toCount Atoms Chapter 4 Calculating with Moles, continued • An element’s molar mass can be used as a conversion factor. • The diagram below shows how to set up the conversion factor, depending on whether you want to convert from amount to mass or the other way around.

Section 4 Using Moles toCount Atoms Chapter 4 Math Skills Converting Amount to Mass Determine the mass in grams of 5.50 mol of iron. 1. List the given and unknown values. Given:amount of iron = 5.50 mol Fe molar mass of iron = 55.85 g/mol FeUnknown: mass of iron = ? g Fe

Cross-Disciplinary: Seeing Atoms - The STM