Topic 2: Elements, Compounds and Mixtures - Subtopic 2: Bonding
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What is an ion?
An ion is an atom or molecule which has become charged through the loss or gain of one or more electron(s).
What happens when metals form ions?
Metals form positive ions (cations) when they react because they lose electrons, leaving them with an overall positive charge.
What happens when non-metals form ions?
Non-metals form negative ions (anions) when they react because they gain electrons, leaving them with an overall negative charge.
What are metalloids?
Elements that display properties of both metals and non-metals, also called semi-metals.
How is the Periodic Table organized in terms of periods and groups?
The table is arranged in vertical columns called groups and horizontal rows called periods.
What do periods in the Periodic Table represent?
Periods are horizontal rows that show the number of shells of electrons an atom has. For example, elements in Period 2 have two electron shells.
What do groups in the Periodic Table represent?
Groups are vertical columns that show how many outer electrons each atom has. For example, Group 4 elements have atoms with 4 electrons in the outermost shell.
What are some alternative names for certain groups in the Periodic Table?
Group 1 is also known as the ‘alkali metals’, Group 7 is also known as the ‘halogens’, and Group 0 is also known as the ‘noble gases’.
How do electrons occupy shells in an atom?
Electrons first occupy the shell closest to the nucleus (maximum 2 electrons), then fill additional shells when a shell becomes full.
How many electrons can the first three electron shells hold?
The first shell can hold 2 electrons, while the second and third shells can each hold 8 electrons.
What is the valence shell?
The outermost shell of an atom is called the valence shell, and an atom is much more stable if this shell is completely filled with electrons.
How do atoms achieve a full outer shell of electrons?
Atoms can gain electrons (non-metals), lose electrons (metals), or share electrons (covalent bonds) to achieve a full outer shell.
How is electron configuration written using number notation?
By writing the number of electrons in each shell separated by commas or periods, starting with the innermost shell (e.g., 2.8.1 for sodium).
What is the relationship between an element’s group number and its electron configuration?
Elements in the same group have the same number of outer shell electrons. For example, 2.2, 2.8.2, and 2.8.8.2 all show Group 2 elements as they all end in ‘2’.
What is an ionic bond?
The strong electrostatic forces of attraction between oppositely charged ions, typically occurring between a metal and a non-metal.
How is a sodium chloride (NaCl) ionic bond formed?
Sodium loses one electron to form Na+ (1+), and chlorine gains one electron to form Cl- (1-), with the oppositely charged ions attracting each other.
How is a magnesium oxide (MgO) ionic bond formed?
Magnesium loses two electrons to form Mg2+ (2+), and oxygen gains two electrons to form O2- (2-), with the oppositely charged ions attracting each other.
What are the advantages of dot and cross diagrams for showing ionic compounds?
They are useful for illustrating the transfer of electrons and indicate from which atom the bonding electrons come.
What are the disadvantages of dot and cross diagrams for showing ionic compounds?
They fail to illustrate the 3D arrangements of atoms and electron shells, and don’t indicate the relative sizes of the atoms.
What are the advantages of ball and stick models for ionic compounds?
They are useful for illustrating the arrangement of atoms/ions in 3D space and for visualizing the shape of an ionic compound.
What are the disadvantages of ball and stick models for ionic compounds?
They fail to indicate the movement of electrons, show ions placed far apart, don’t show accurate ion sizes, don’t show electrostatic forces, and don’t show ion charges.
What is a covalent bond?
When non-metal atoms share pairs of electrons with other non-metal atoms to obtain a full outer shell of electrons.
How strong are covalent bonds?
Covalent bonds between atoms are very strong.
What is a molecule?
When two or more atoms are chemically bonded together, they form ‘molecules’.